JP6073520B1 - Photocatalyst material and method for producing the same - Google Patents

Abstract

Provided is a photocatalyst material capable of expressing high photocatalytic activity under irradiation with visible light, that is, capable of photodegrading water with high efficiency and having a very high hydrogen generation ability. A substrate 90 and a photocatalyst layer 70 fixed to the substrate 90 are provided. The photocatalyst layer 70 includes first photocatalyst particles 10 that are responsive to visible light for hydrogen generation and oxygen generation. Visible light responsive second photocatalyst particles 20, and provided between the first photocatalyst particles 10 and the second photocatalyst particles 20, the electron energy level at the top of the valence band of the first photocatalyst particles 10 Conductive particles 40 having a Fermi level at a position that is more negative than the electron energy level at the lower end of the conduction band of the second photocatalyst particle 20 and capable of storing electrons and holes. The photocatalyst material 100 containing. In the photocatalyst layer 70, the conductive particles 40 are arranged so as to be connected to the first photocatalyst particles 10 and the second photocatalyst particles 20. [Selection] Figure 1

Description

  The present invention relates to a photocatalyst material in which a photocatalyst layer containing photocatalyst particles for hydrogen generation and oxygen generation photocatalyst particles capable of photolysis of water by visible light is immobilized on a substrate, and a method for producing the same.

  A visible light responsive photocatalyst is a photocatalyst that can use visible light contained in a large amount of sunlight. This visible light responsive photocatalyst is expected to be applied to hydrogen production by photolysis of organic substances and water. Among these, a photocatalyst for water splitting for the purpose of producing hydrogen has attracted attention as a photocatalyst used in a method for producing hydrogen using renewable energy. As a result, the demand for a photocatalyst for water splitting that provides high activity is increasing year by year.

  In WO2014 / 046305 (Patent Document 1), a photocatalyst material comprising a base material and a photocatalyst layer immobilized on the base material, wherein the photocatalyst layer has a primary particle diameter of 100 nm or less. Examples include those that include visible light responsive photocatalyst particles for hydrogen generation and visible light responsive photocatalyst particles for oxygen generation. In this example, the visible light responsive photocatalyst particles for hydrogen generation and the visible light responsive photocatalyst particles for oxygen generation are in contact with each other. According to Patent Document 1, it is reported that this photocatalyst material has high hydrogen generation ability. On the other hand, further improvement is required for the hydrogen generation ability of the photocatalyst material.

  Japanese Unexamined Patent Application Publication No. 2014-046236 (Patent Document 2) includes first semiconductor particles formed by bonding first metal particles and second semiconductor particles formed by bonding second metal particles. Semiconductor heteroparticles are illustrated. In this example, the potential at the lower end of the conduction band of the first semiconductor particle is more negative (base, that is, closer to the vacuum level) than the potential at the upper end of the valence band of the second semiconductor particle. The work function of the second metal particle with respect to the standard hydrogen electrode (NHE) is independently equal to one of the potential at the lower end of the conduction band of the first semiconductor particle and the potential at the upper end of the valence band of the second semiconductor particle. Or located between these potentials. According to Patent Document 2, it is reported that the semiconductor hetero particles exhibit a photocatalytic function without using an electron mediator. Patent Document 2 specifically evaluates the photocatalytic activity of semiconductor hetero particles in the case of using a dispersion obtained by dispersing the particles in water.

  JP 2012-187520 A (Patent Document 3) discloses a photocatalyst-immobilized product for water splitting having a photocatalyst layer on a substrate, wherein the photocatalyst layer is a nitride or an oxynitride. And a photocatalyst-immobilized product comprising a promoter supported on a visible light responsive optical semiconductor and a hydrophilic inorganic material.

WO2014 / 046305 JP 2014-046236 A JP 2012-187520 A

  The present inventors have recently made the photocatalyst layer comprising visible light responsive photocatalyst particles for hydrogen generation and visible light responsive photocatalyst particles for oxygen generation further contain conductive particles, so that the visible light for hydrogen generation is contained. It was found that a photocatalyst material capable of exhibiting high photocatalytic activity under visible light irradiation can be obtained by connecting the photoresponsive photocatalyst particles and the visible light responsive photocatalyst particles for oxygen generation. According to the present invention, it is possible to obtain a photocatalyst material capable of photolyzing water with high efficiency and having significantly improved hydrogen generation ability. The present invention is based on such knowledge.

  Accordingly, an object of the present invention is to provide a photocatalyst material having enhanced hydrogen generation ability under visible light irradiation.

  The photocatalyst material according to the present invention is a photocatalyst material comprising a base material and a photocatalyst layer fixed to the base material, wherein the photocatalyst layer is a first visible light responsive type for hydrogen generation. Photocatalyst particles, visible light responsive second photocatalyst particles for oxygen generation, and the valence band of the first photocatalyst particles provided between the first photocatalyst particles and the second photocatalyst particles. Conductivity capable of storing electrons and holes, which is a position that is more negative than the electron energy level at the upper end and has a Fermi level at a position that is more positive than the electron energy level at the lower end of the conduction band of the second photocatalyst particle. In the photocatalyst layer, the conductive particles are arranged so as to be connected to the first photocatalyst particles and the second photocatalyst particles. It is.

  According to the photocatalyst material according to the present invention, it is possible to obtain a photocatalyst material that is capable of water decomposition exhibiting a high photocatalytic activity under irradiation with visible light and has an increased hydrogen generation ability.

It is a schematic cross section which shows the photocatalyst material by this invention. It is a schematic cross section for demonstrating the electrolysis particle | grains and water photolysis mechanism which concern on this invention. It is a schematic cross section which shows the photocatalyst material by this invention. It is a schematic cross section which shows the photocatalyst material by this invention. It is a schematic cross section which shows the photocatalyst material by this invention. It is a schematic cross section which shows the photocatalyst material by this invention. It is a schematic cross section which shows the photocatalyst material by this invention. It is a schematic cross section which shows the photocatalyst material by this invention. It is a schematic cross section which shows the photocatalyst material by this invention. It is a schematic cross section which shows the photocatalyst material by this invention. 3 is an SEM image of a photocatalyst layer of the photocatalyst material 3. It is a SEM image of the photocatalyst layer of the photocatalyst material by this invention. It is a SEM image of the photocatalyst layer of the photocatalyst material by this invention. It is a graph which shows the relationship between the photocatalyst material 1 and gas production | generation efficiency. It is a graph which shows the relationship between the photocatalyst material 2 and gas production | generation efficiency. It is a graph which shows the relationship between the photocatalyst material 3 and gas production | generation efficiency. It is a graph which shows the relationship between the photocatalyst material 4 and gas production | generation efficiency. It is a graph which shows the hydrogen and oxygen gas generation speed in the photocatalyst materials 1-4. It is a graph which shows the gas production | generation efficiency of photocatalyst materials 5-8,13. It is a graph which shows the gas production | generation efficiency of the photocatalyst materials 9-13. It is a graph which shows the gas production | generation efficiency of the photocatalyst materials 14-18. It is a graph which shows the gas production | generation efficiency of photocatalyst materials 19-23,30. It is a graph which shows the gas production | generation efficiency of the photocatalyst materials 26-28. It is a graph which shows the gas production | generation efficiency of the photocatalyst materials 19, 24, 25, 30. It is a graph which shows the gas production | generation efficiency of the photocatalyst materials 22 and 29. FIG. It is a figure which shows the relationship between the material of a coating | coated part in the photocatalyst materials 36-46, and the reverse reaction prevention rate based on a hydrogen generation rate. It is a figure which shows the relationship between the material of a coating | coated part in the photocatalyst materials 36-46, and the reverse reaction prevention rate based on an oxygen generation rate. It is a figure which shows the relationship between content of a zirconium oxide in the photocatalyst materials 38-41, 46, and the reverse reaction prevention rate based on a hydrogen generation rate. It is a figure which shows the relationship between content of a zirconium oxide in the photocatalyst materials 38-41, 46, and the reverse reaction prevention rate based on an oxygen generation rate.

Definitions In this specification, “visible light” means electromagnetic waves (light) having a wavelength that can be visually recognized by human eyes. Preferably, it means light containing visible light having a wavelength of 380 nm or longer, more preferably light containing visible light having a wavelength of 420 nm or longer. In addition, as light including visible light, sunlight, condensed sunlight with increased energy density by condensing, or an artificial light source such as a xenon lamp, a halogen lamp, a sodium lamp, a fluorescent lamp, or a light emitting diode is used as a light source. It is possible. Preferably, sunlight that is inexhaustible on the earth is used as the light source. Thereby, visible light occupying about 52% of the sunlight can be used, and hydrogen and oxygen can be efficiently extracted from the water.

  In the present specification, “visible light responsive photocatalyst particles for hydrogen generation” means photocatalyst particles capable of generating hydrogen by a photolysis reaction of water with visible light, and “visible light responsive photocatalyst particles for oxygen generation”. The term “photocatalyst particles” refers to photocatalyst particles capable of generating oxygen by water photolysis reaction with visible light.

  In the present specification, the term “couple” between particles means at least a state in which a plurality of particles are arranged so that holes and / or electrons can move between the particles. For example, it includes embodiments in which the particles are not in physical contact but are arranged so that holes and / or electrons can move. On the other hand, “contact” of particles means a state in which some of the particles are arranged in contact with each other. In a mode in which the particles are in “contact” with each other, a part of the particles are in contact with each other so that holes and / or electrons can move between the particles, that is, the particles are in contact with each other. The state of being electrically connected is included. Further, “bonding” particles means a state in which particles are arranged in contact with each other more firmly than in the case of “contact”. “Join” includes, for example, a chemically bonded state.

With reference to Figure 1 the overall construction of a photocatalytic material by the photocatalyst material present invention will be described.
The photocatalyst material 100 includes a base material 90 and a photocatalyst layer 70 fixed to the base material 90. The photocatalyst layer 70 includes the first photocatalyst particles 10 for visible light response type for hydrogen generation (hereinafter also simply referred to as “first photocatalyst particles”) and the second photocatalyst particles 20 for visible light response type for oxygen generation ( Hereinafter, it is also simply referred to as “second photocatalyst particles”) and conductive particles 40. In the photocatalyst layer 70, the conductive particles 40 are disposed so as to be connected to the first photocatalyst particles 10 and the second photocatalyst particles 20. Since the photocatalyst material according to the present invention has the above-described configuration, it can exhibit high photocatalytic activity under visible light irradiation, enables water to be photolyzed with high efficiency, and generates extremely high hydrogen. Have the ability.

Substrate 90 contained in the photocatalyst material according to the substrate present invention may be any one capable of immobilizing the photocatalyst layer 70 on the surface thereof. Specific examples of such a substrate 90 include an organic substrate and an inorganic substrate. Examples of the organic substrate include a plastic substrate. Examples of the inorganic base material include a ceramic base material such as an alumina substrate, a glass base material such as soda lime glass and borosilicate glass, and a quartz base material. For example, a base material that is not easily decomposed by heating at 250 ° C. or higher or 300 ° C. or higher is more preferable. You may use the base material which has a light transmittance.

  Further, a metal substrate may be used as the substrate 90. Specific examples of the metal include titanium, aluminum, iron, and stainless steel. Practically, the above organic substance or inorganic substance is preferable to metal.

  In the photocatalyst material according to the present invention, an insulating base material can be used as the base material 90.

  The base material 90 should just have a shape in which the photocatalyst layer 70 can be fixed to the surface by drying or baking. Specific examples of such a substrate 90 include a flat plate having a smooth surface (for example, a glass substrate or an alumina substrate), a surface porous flat plate (for example, anodized alumina), a porous body (for example, porous ceramics), A fiber body (for example, glass fiber, carbon fiber) or the like can be preferably used. As the fibrous body, more preferably, a glass fiber having high light transmittance can be used. Thereby, light can be transmitted into the layer rather than the light irradiation surface of the fibrous body, and an increase in light absorption can be expected. Further, the surface shape of the substrate 90 may be a wavy shape, a comb shape, a fiber shape, or a mesh shape.

  The base material 90 may have a plurality of holes. The diameter of each hole is preferably 0.1 to 30 μm, for example. For example, these pores are preferably arranged as continuous pores. Thereby, for example, after hydrogen gas generated by the water splitting reaction on the surface of the photocatalyst particles (10, 20) disposed inside the photocatalyst layer 70 diffuses through pores 71 (described later) inside the photocatalyst layer 70, For example, it is possible to reach the outside of the photocatalyst layer 70 through these holes having openings larger than the pores 71, and it is possible to generate hydrogen gas more efficiently.

Photocatalyst layer As shown in FIG. 1, in the photocatalyst material 100, the conductive particles 40 are formed with any of the first photocatalyst particles 10 and the second photocatalyst particles 20 at any part (point, surface, etc.) of the surface. In contact. In the photocatalyst layer 70, the surface of the conductive particles 40 includes a first region 40a, a second region 40b, and a third region 40c. In the first region 40a, the conductive particles 40 and the first photocatalyst particles 10 are in contact. In the second region 40b, the conductive particles 40 and the second photocatalyst particles 20 are in contact with each other. The third region 40 c is a region other than the first region 40 a and the second region 40 b on the surface of the conductive particle 40. That is, in the third region 40c, the conductive particles 40 do not contact either the first photocatalyst particle 10 or the second photocatalyst particle 20.

  In the photocatalyst layer 70, the first photocatalyst particle 10 and the second photocatalyst particle 20 are connected via the conductive particle 40, so that the excitation positive generated in the valence band VB <b> 10 of the first photocatalyst particle 10. The degree of electrical connection through the conductive particles 40 between the holes and the excited electrons generated in the conduction band CB20 of the second photocatalyst particles 20 becomes stronger. Therefore, in the photocatalyst material 100, a charge recombination reaction described later between the photoexcited hole and the photoexcited electron in the conductive particle 40 occurs more reliably. As a result, the photocatalytic activity of the photocatalyst layer 70 can be more reliably increased, and the hydrogen generation ability of the photocatalyst layer 70 is more reliably improved.

  In the present invention, the photocatalyst layer 70 may be a dense continuous layer. The photocatalyst layer 70 may have a discontinuous part, for example. For example, the photocatalyst layer 70 may be dispersed in an island shape on the surface of the base material 90. The photocatalyst layer 70 may be in a wave shape, a comb shape, a fiber shape, a mesh shape, or the like.

  The photocatalyst layer 70 has, for example, pores 71 through which water, hydrogen, and oxygen gas can diffuse. For example, the pore 71 is disposed between the first photocatalyst particle 10, the second photocatalyst particle 20, and the conductive particle 40. By passing through the pores 71, not only the surface of the photocatalyst layer 70 but also the photocatalyst particles located inside thereof can come into contact with water and light.

In the present invention, the thickness of the photocatalyst layer 70 is preferably 0.1 μm or more and 50 μm or less. A more preferable thickness of the photocatalyst layer 70 is 0.2 μm or more and 30 μm or less.
Here, the thickness of the photocatalyst layer 70 can be obtained, for example, by observation with a scanning electron microscope of a cross section of the photocatalyst material. Specifically, for example, the distance from a horizontal tangent at a certain point on the surface of the substrate 90 to the top of the photocatalyst layer 70 at a perpendicular to the tangent. For example, when the substrate 90 is a flat plate as shown in FIG. 1 or the like, the thickness of the photocatalyst layer 70 is the distance from the surface of the substrate 90 to the top of the photocatalyst layer 70 in the vertical direction. When the surface of the substrate 90 is like a fiber, the thickness of the photocatalyst layer 70 is a distance from a horizontal tangent at a certain point on the fiber surface to the top of the photocatalyst layer 70 at a perpendicular to the tangent. It is.

Visible light responsive photocatalyst particles for hydrogen generation (first photocatalyst particles)
The first photocatalytic particle 10 is a semiconductor particle having an optical band gap. When the first photocatalyst particle 10 absorbs visible light, excited electrons are generated in the electron acceptor level existing in the conduction band or the band gap by electronic transition such as interband transition in the first photocatalyst particle 10. In addition, excited holes are generated in the electron donor level existing in the valence band or the band gap. The first photocatalyst particle 10 is a photocatalytic material in which each of the excited electrons and excited holes can reduce and oxidize the reaction target. That is, the first photocatalyst particle 10 is a photocatalyst material that can generate hydrogen by reducing water, for example, by excited electrons generated by irradiation with visible light. The electron acceptor level existing in the conduction band or band gap of the first photocatalyst particle 10 is, for example, in a position more negative than the reduction potential of water (0 V vs. NHE (standard hydrogen electrode potential) at pH = 0). is there. Moreover, the electron donor level which exists in the valence band or band gap of the 1st photocatalyst particle 10 exists in a position more positive than the conduction band position of the 2nd photocatalyst particle, for example.

Preferred examples of the first photocatalyst particles 10 include Rh-doped SrTiO ₃ (SrTi _1-x Rh _x O ₃ : x = 0.002 to 0.1), Ir-doped SrTiO ₃ (SrTi _1-x Ir _x O3: x = 0.002 to 0.1), Cr-doped SrTiO ₃ (SrTi _1-x Cr _x O ₃ : x = 0.002 to 0.1), Cr and Ta-doped SrTiO ₃ (SrTi _1-xy Cr) _x Ta _y O ₃ : x = 0.002 to 0.1, y = 0.002 to 0.1), La and Rh-doped SrTiO ₃ (Sr _1-x La _x Ti _1-y Rh _y O ₃ : x = 0.005-0.2, y = 0.005-0.2) and the like perovskite type SrTiO ₃ , Cu ₂ O, CuO, CaFe ₂ O ₄ , Ni doped with at least one kind of transition metal or noble metal Transition metals such as O, Bi ₂ O ₃ , BiOX (X = Cl, Br, I), GaN-ZnO solid solution, LaTiO ₂ N, BaTaO ₂ N, BaNbO ₂ N, TaON, Ta ₃ N ₅ , Ge ₃ N ₄ Alternatively, an oxynitride or nitride containing a typical metal, CuGaS ₂ , CuInS ₂ , Cu (Ga, In) S ₂ , CuGaSe ₂ , CuInSe ₂ , Cu (Ga, In) Se ₂ , Cu ₂ ZnSnS ₄ (CZTS) , Cu ₂ ZnSn (S, Se) ₄ , copper complex selenide containing typical metals such as Ga, In, Al, La ₅ Ti ₂ CuS ₅ O ₇ , La ₅ Ti ₂ AgS ₅ O ₇ , La ₅ Ti _{2 CuSe 5 O 7, La 5} Ti 2 AgSe 1 or more selected from ₅ O ₇ group consisting of acid sulfate selenide and the like.

More preferable examples of the first photocatalyst particles 10 include Rh-doped SrTiO ₃ (SrTi _1-x Rh _x O 3: x = 0.005 to 0.05), Ir-doped SrTiO ₃ (SrTi _1-x Ir _x O 3: x = 0.005 to 0.05), Cr-doped SrTiO ₃ (SrTi _1-x Cr _x O ₃ : x = 0.002 to 0.1), Cr and Ta-doped SrTiO ₃ (SrTi _1-xy Cr) _x Ta _y O ₃ : x = 0.002 to 0.1, y = 0.002 to 0.1), La and Rh-doped SrTiO ₃ (Sr _1-x La _x Ti _1-y Rh _y O ₃ : x Perovskite type SrTiO ₃ , Cu ₂ O, CuO, CaFe ₂ O ₄ doped with at least one kind of transition metal or noble metal such as _{, NiO, Bi 2 O 3,} BiOX (X = Cl, Br, I), GaN-ZnO solid _{solution, LaTiO 2 N, BaTaO 2 N} , BaNbO 2 N, TaON, Ta 3 N 5, Ge 3 N 4, CuGaS 2 , CuInS ₂ , Cu (Ga, In) S ₂ , CuGaSe ₂ , CuInSe ₂ , Cu (Ga, In) Se ₂ , Cu ₂ ZnSnS ₄ (CZTS), Cu ₂ ZnSn (S, Se) _4, La ₅ Ti ₂ CuS ₅ O ₇ and the metal-doped _compounds, one or more can be mentioned which is selected from the group consisting of La ₅ Ti 2 _{AgS 5 O 7} and oxysulfide of the metal-doped compounds.

As the most preferable examples of the first photocatalyst particles 10, Rh-doped SrTiO ₃ (SrTi _1-x Rh _x O ₃ : x = 0.01 to 0.04), Cr-doped SrTiO ₃ (SrTi _1-x Cr _x O ₃ : x = 0.002 to 0.1), Cr and Ta doped SrTiO ₃ (SrTi _1-xy Cr _x Ta _y O ₃ : x = 0.002 to 0.1, y = 0.002 to 0 .1), transition metals such as La and Rh-doped SrTiO ₃ (Sr _1-x La _x Ti _1-y Rh _y O ₃ : x = 0.005 to 0.2, y = 0.005 to 0.2) Alternatively, one or more selected from the group consisting of perovskite-type SrTiO ₃ , TaON, and Ta ₃ N ₅ doped with at least one kind of noble metal can be used.

Preferably has an average primary particle diameter of average primary particle diameter first photocatalyst particles 10 of the first photocatalyst particles is 1000nm or less. By having such a small particle size, in the first photocatalyst particle 10, the surface area per unit weight that can contact with water is increased. Thereby, the reduction reaction site of water increases, and as a result, highly efficient hydrogen generation becomes possible. More preferably, the average primary particle diameter of the first photocatalyst particles 10 is 30 nm or more.

Visible light responsive photocatalyst particles for oxygen generation (second photocatalyst particles)
The second photocatalytic particle 20 is a semiconductor particle having an optical band gap. When the second photocatalyst particles 20 absorb visible light, excited electrons are generated in the conduction band and excited holes are generated in the valence band due to electronic transition such as interband transition in the second photocatalyst particles 20. The second photocatalyst particle 20 is a photocatalytic material in which each of the excited electrons and excited holes can reduce and oxidize the reaction target. That is, the second photocatalyst particle 20 is a photocatalyst material in which excited holes generated by, for example, irradiation with visible light can oxidize water to generate oxygen. For example, the valence band of the second photocatalyst particle 20 is at a position more positive than the oxidation potential of water (+1.23 V vs. NHE (standard hydrogen electrode potential) at pH = 0). In addition, the conduction band of the second photocatalyst particle 20 is at a position that is more negative than the valence band position of the first photocatalyst particle, for example.

Preferred examples of the second photocatalyst particles 20 include BiVO ₄ , X-doped BiVO ₄ (X: Mo, W), SnNb ₂ O ₆ , WO ₃ , Bi ₂ WO ₆ , Fe ₂ TiO ₅ , Fe ₂ O ₃ , From oxynitrides or nitrides containing transition metals such as Bi ₂ MoO ₆ , GaN-ZnO solid solution, LaTiO ₂ N, BaTaO ₂ N, BaNbO ₂ N, TaON, Ta ₃ N ₅ , Ge ₃ N _4, etc. One or more selected from the group consisting of:

More preferable examples of the second photocatalyst particles 20 include BiVO ₄ , X-doped BiVO ₄ (X: Mo, W), SnNb ₂ O ₆ , WO ₃ , Bi ₂ WO ₆ , Bi ₂ MoO ₆ , Fe ₂ O _3. GaN-ZnO solid solution, LaTiO ₂ N, BaTaO ₂ N, BaNbO ₂ N, TaON, Ta ₃ N ₅ , Ge ₃ N ₄ or more.

The most preferable example of the second photocatalyst particle 20 is a kind selected from the group consisting of BiVO ₄ , Mo-doped BiVO ₄ , WO ₃ , SnNb ₂ O ₆ , Bi ₂ WO ₆ , BaTaO ₂ N, and Fe ₂ O _3. The above is mentioned.

The average primary particle diameter of the second average primary particle diameter second photocatalyst particles 20 of photocatalyst particles is preferably 1000nm or less. By having such a small particle size, in the second photocatalyst particle 20, the surface area per unit weight that can come into contact with water increases. Thereby, the oxidation reaction site of water increases, As a result, highly efficient oxygen generation is attained. More preferably, the average primary particle diameter of the second photocatalyst particles 20 is 30 nm or more.

Evaluation Method of Average Primary Particle Diameter of First and Second Photocatalyst Particles As an evaluation method of the average primary particle diameter of the first photocatalyst particle 10 and the second photocatalyst particle 20, for example, a scanning electron microscope (Hitachi Corporation) “S-4100” (hereinafter also referred to as “SEM”) manufactured by Seisakusho Co., Ltd.) can be defined as an average value by circular approximation of 50 crystal grains when observed at a magnification of 40000 times.

Conductive Particles FIG. 2 is a schematic cross-sectional view for explaining the photolysis mechanism of conductive particles and water according to the present invention. The conductive particles 40 will be described with reference to FIG.

(Definition)
In the present invention, the conductive particle 40 is a position that is more negative than the electron energy level at the upper end of the valence band VB10 of the first photocatalyst particle 10, and the electron energy level at the lower end of the conduction band CB20 of the second photocatalyst particle 20. It is a conductive particle having a Fermi level at a position more positive than the position and capable of storing electrons and holes. When the conductive particles 40 have such a specific Fermi level, the photodecomposition of water by the photocatalyst material 100 can be remarkably improved by a mechanism described later. Note that the Fermi level of the conductive particles can also be expressed by using the potential as a reference instead of the electron energy level. In this case, the conductive particle 40 has the valence band VB10 of the first photocatalyst particle 10. The Fermi level has a negative potential from the upper end and a positive potential from the lower end of the conduction band CB20 of the second photocatalyst particle 20.

(material)
Examples of preferable materials for the conductive particles 40 include metals such as gold, silver, copper, nickel, rhodium and palladium, carbon materials, nitrides such as TiN, carbides such as TiC, manganese oxides (MnO ₂ , AMnO ₃ ( A: Ca or Sr), B-doped AMnO ₃ (A: Ca or Sr, B: La ³⁺ , Y ³⁺ , Bi ³⁺ , Nb ⁵⁺ , or Ta ⁵⁺ )), tin-doped indium oxide (ITO), metal (B, Al , Ga) doped zinc oxide, fluorine doped tin oxide, antimony doped tin oxide, ruthenium oxide, iridium oxide, rhodium oxide, spinel oxide AB ₂ O ₄ (A = Fe, Ni, Mn, Co, Zn, etc., B = One or more selected from the group consisting of conductive metal oxides such as Fe, Co, Mn, etc. A = B or A ≠ B) And the like. Among these, it is selected from the group consisting of conductive metal oxides such as gold, carbon material, ITO, and metal (B, Al, Ga) doped zinc oxide, ruthenium oxide, iridium oxide, and magnetite (Fe ₃ O ₄ ). One or more of these are more preferred. As the carbon material, for example, carbon black, ketjen black, acetylene black, channel black, furnace black, thermal black, lamp black and the like can be used.

  When the conductive particles and the photocatalyst particles are both metal oxides, since the photocatalyst particles and the conductive particles are metal oxides, the conductive particles can obtain an excellent binder effect, Contact between the particles and the photocatalyst particles can be made stronger. In addition, when inorganic materials such as glass and alumina, especially metal oxides are used as the material of the base material, and the conductive particle material is also a metal oxide, a metal-oxygen bond is formed between the base material and the conductive particles. Is done. Therefore, the adhesion between the conductive particles and the base material is improved. As a result, it is possible to improve the mechanical strength of the entire photocatalyst material. Therefore, when the photocatalyst material is mounted on the hydrogen production module, the photocatalyst layer can suppress the detachment of photocatalyst particles due to a load caused by running water, and can function as a photocatalyst film having excellent long-term durability. Become. Moreover, as conductive particles made of a metal oxide, those having a crystal structure are preferable to those having an amorphous structure. Thereby, high electroconductivity and high stability with respect to oxidation reduction are obtained.

  Note that barium, cesium, and sodium, which are generally known as conductive materials, have a small work function and do not have the above-described Fermi level. Therefore, these materials are not included in the conductive particles 40 in the present invention.

(Shape and particle state)
The conductive particles 40 may be in any particle state. As shown in FIG. 1, the conductive particles 40 are, for example, so-called primary particles, and even if the first photocatalyst particles 10 and the second photocatalyst particles 20 are in contact with one conductive particle 40. Good. Alternatively, as shown in FIG. 10 described later, for example, so-called secondary particles in which primary particles are aggregated are used as the conductive particles 40, and a plurality of first photocatalyst particles 10 and second photocatalyst particles 20 are combined. You may connect by the aggregate | assembly of the electroconductive particle 40. FIG. The conductive particles 40 may be in a state where a plurality of primary particles and / or a single or a plurality of secondary particles are joined, for example, by heating, as shown in FIG. 9 described later. Any of the above embodiments is included in a state in which the conductive particles 40, the first photocatalyst particles 10 and the second photocatalyst particles 20 are connected via the same conductive particles 40.

  In the present invention, the conductive particles 40 may have any shape. The shape of the conductive particles 40 is, for example, an isotropic shape (such as a spherical shape or a substantially polygonal shape) or an anisotropic shape (such as a columnar shape, a rod shape, a plate shape, or a flake shape). As anisotropically shaped particles, for example, conductive wires can be used. Examples of the conductive wire include particles having a rod-like or needle-like form.

(Average primary particle size)
In the present invention, the average primary particle diameter of the conductive particles 40 is preferably smaller than the average primary particle diameter of each of the first photocatalyst particles 10 and the second photocatalyst particles 20. Thereby, in the photocatalyst layer 70, for example, the first and second photocatalyst particles 10 and 20 can be effectively irradiated with light. Further, when the average primary particle diameter of the conductive particles 40 is smaller than the average primary particle diameter of each of the first photocatalyst particles 10 and the second photocatalyst particles 20, each of the base material 90 and the photocatalyst layer 70 is configured. The number of contact points per unit area with the particles can be increased. Therefore, the adhesion between the photocatalyst layer 70 and the base material 90 can be improved.

  Further, the average primary particle diameter of the conductive particles 40 can be appropriately selected within a range in which light irradiation to the first photocatalyst particle 10 and the second photocatalyst particle 20 is ensured in the photocatalyst layer 70. For example, when using light-transmitting particles as the conductive particles 40, particles having a relatively large particle diameter can be used. On the other hand, when using non-light-transmitting particles as the conductive particles 40, it is preferable to use particles having a smaller particle diameter.

  The average primary particle diameter of the conductive particles 40 is, for example, preferably 1 nm to 1000 nm, more preferably 5 nm to 500 nm, and even more preferably 5 nm to 200 nm. Thereby, in the photocatalyst layer 70, the first photocatalyst particles 10 and the second photocatalyst particles 20 can be effectively irradiated with visible light. In the photocatalyst layer 70, for example, the conductive particles 40 and the photocatalyst particles (10, 20) can be satisfactorily brought into contact with each other. In addition, appropriate pores 71 can be formed in the photocatalytic layer 70. In addition, by increasing the average primary particle diameter of the conductive particles within the above range, the probability that a charge recombination reaction occurs between the first photocatalyst particle 10 and the second photocatalyst particle 20 is increased. Can do. As a result, high water splitting activity can be more reliably obtained in the photocatalyst material.

  The average primary particle diameter of the conductive particles 40 is particularly preferably 10 nm or more and 200 nm or less. By setting the particle size within this range, the conductive particles 40 can not only connect the first photocatalyst particles 10 and the second photocatalyst particles 20, but also exhibit an excellent function as a binder, The adhesion between particles can be improved.

  When the conductive particles 40 are isotropic shaped particles, the average primary particle diameter is, for example, preferably 1 nm to 1000 nm, more preferably 5 nm to 500 nm, still more preferably 5 nm to 200 nm, and even more preferably 10 nm to 200 nm. Is particularly preferred. By having such an average primary particle size, the conductive particles 40 and the photocatalyst particles (10, 20) can be efficiently contacted. Further, the conductive particles 40 suppress the hindering of the light absorption of the photocatalyst particles (10, 20). In the present invention, when the conductive particles 40 are isotropic shaped particles, for example, the area of the conductive particles obtained by observing the conductive particles 40 with SEM or TEM is converted into the area of a circle. The diameter obtained may be the average primary particle diameter. Alternatively, the diameter of the maximum cross section of the conductive particles 40 may be the average primary particle diameter of the conductive particles 40.

  When the conductive particles 40 are anisotropic particles, the aspect ratio (major axis diameter / minor axis diameter) of the conductive particles 40 is preferably 5 or more and 1000 or less. By setting it as such an aspect ratio, the probability that the 1st photocatalyst particle 10 and the 2nd photocatalyst particle 20, and an electroconductive wire can fully be made high. Therefore, the charge recombination reaction described later is promoted. As a result, efficient photolysis of water becomes possible. Furthermore, when the anisotropic conductive particles 40 are used, the binder effect by the conductive particles 40 can be enhanced.

When a conductive wire is used as the anisotropic conductive particles 40, the average primary particle diameter is preferably, for example, 1 nm to 1000 nm, and preferably 5 nm to 200 nm. Here, the average primary particle diameter of the conductive wire refers to a diameter when a cross section having a minimum cross-sectional area of the conductive wire is approximated by a circle.
The length of the long axis of the conductive wire is not particularly limited, but is preferably 10 nm or more and 10,000 nm or less. By having such a shape and size, it is possible to efficiently contact the conductive wire and the photocatalyst particles (10, 20). Further, the conductive particles 40 suppress the hindering of the light absorption of the photocatalyst particles (10, 20). Moreover, the binder effect by the electroconductive particle 40 can be improved.

  When a conductive plate having a plate-like or flaky shape is used as the anisotropic conductive particle 40, the major axis diameter of the plate surface or the flaky piece is preferably 20 nm or more and 1000 nm or less. The average primary particle diameter of the plate surface or flakes is preferably 1 nm or more and 1000 nm or less. Here, the average primary particle diameter of the conductive plate refers to, for example, the diameter of a conductive plate obtained by circularly approximating a cross section having a minimum cross-sectional area. The aspect ratio (major axis diameter / minor axis diameter) of the conductive plate is preferably, for example, 3 or more and 5000 or less, and more preferably 10 or more and 1000 or less. By using a conductive plate having such a shape and size as the conductive particles 40, the photocatalyst particles (10, 20) and the conductive particles 40 can be efficiently contacted. Further, the conductive particles 40 suppress the hindering of the light absorption of the photocatalyst particles (10, 20). Moreover, the binder effect by the electroconductive particle 40 can also be improved.

(Conductivity / Volume resistivity)
The conductivity of the conductive particles 40 is preferably 0.1 Scm ⁻¹ or more. The volume resistivity of the conductive particles 40 is preferably 10 Ωcm or less, for example.

(Content)
In the present invention, the photocatalyst material preferably contains the conductive particles 40 in an amount that can increase the number of electrical connection points between the first photocatalyst particles 10 and the second photocatalyst particles 20. Moreover, it is preferable that the photocatalyst material contains the conductive particles 40 in an amount that does not hinder the light absorption of the first photocatalyst particles 10 and the second photocatalyst particles 20. The content can be appropriately set in consideration of the average primary particle diameter of the first photocatalyst particles 10, the second photocatalyst particles 20 and the conductive particles 40, or the specific gravity of the conductive particles 40. The content is preferably set as appropriate within a range in which the pores 71 can be formed in the photocatalyst layer 70, for example. For example, the conductive particles 40 are preferably included in an amount of 1 wt% to 99 wt% with respect to the total content of the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40. The ratio of the content of the conductive particles 40 is more preferably 5 wt% or more and 60 wt% or less, and 5 wt% or more and 50 wt% or less.

(Mechanism of water photolysis)
The property and function of the conductive particles 40 and the mechanism of photodecomposition of water by the photocatalyst material 100 will be described again with reference to FIG.
As shown in FIG. 2, by irradiating visible light, excited holes generated in the valence band VB10 of the first photocatalyst particle 10 are diffused to the surface of the first photocatalyst particle 10, and the valence band VB10. It is considered that the particles move into the conductive particles 40 having the Fermi level at a position more negative than the electron energy level at the upper end. Further, by irradiating visible light, the excited electrons generated in the conduction band CB20 of the second photocatalyst particle 20 diffuse to the surface of the second photocatalyst particle 20 and are more positive than the electron energy level at the lower end of the conduction band CB20. It is considered that the particles move into the conductive particles 40 having the Fermi level at various positions. Then, the photoexcited holes generated in the valence band VB10 of the first photocatalyst particle 10 stored in the conductive particles 40 react with the photoexcited electrons generated in the conduction band CB20 of the second photocatalyst particle 20. The charge recombination reaction occurs, and these two excited carriers are considered to disappear. By this charge recombination reaction, photoexcited holes and photoexcited electrons, which have not been involved in the conventional photodecomposition reaction of water, but rather tend to reduce the photocatalytic activity of individual particles in the photodecomposition reaction of water, are highly efficient. It is possible to extinguish, and this is thought to enable the water photolysis reaction to occur efficiently. That is, the extinction of the photoexcited holes generated in the first photocatalyst particle 10 and the photoexcited electrons generated in the second photocatalyst particle 20 by the charge recombination reaction was generated in the conduction band CB10 of the first photocatalyst particle 10. It is thought that it is possible to increase the efficiency of water reduction reaction by photoexcited electrons. As a result, the first photocatalyst particles 10 and the second photocatalyst particles 20 that are electrically connected by the conductive particles 40 can exhibit high photocatalytic activity, and an improvement in hydrogen generation ability is realized. It is done. In FIG. 2, f1 represents the Fermi level of tin-doped indium oxide (ITO) as the conductive particle 40, and f2 represents the Fermi level of gold (Au) as the conductive particle 40. Further, the above explanation is a hypothesis, and the present invention is not limitedly understood thereby.

(Work function)
In the present invention, the Fermi level of the conductive particle 40 can be estimated using a work function that is an energy difference between the vacuum level and the Fermi level. The work function can be obtained, for example, by potential measurement using a Kelvin probe force microscope (KPFM).

Covering Part In the present invention, the photocatalyst layer 70 of the photocatalyst material 100 preferably further includes a covering part that covers at least a part of the third region 40 c of the conductive particle 40. When the photocatalyst layer 70 has the covering portion 60, for example, the reverse reaction described later is prevented, the generated hydrogen gas and oxygen gas are accelerated, the conductive particles 40, and the first and second photocatalyst particles. The peeling from the base materials 10 and 20 can be prevented, or the oxidation of the conductive particles can be prevented. Therefore, by providing the covering portion 60, the durability of the photocatalyst layer 70 can be enhanced, and the water splitting performance can be enhanced. The activity and stability of the conductive particles in the water splitting reaction in water can be improved.

  The covering portion preferably covers almost all of the third region 40c of the conductive particles 40, and more preferably covers all. Thus, in the aspect in which the coating portion covers only the third region 40c of the conductive particle 40, the surfaces of the first photocatalyst particle 10 and the second photocatalyst particle 20 are not covered with the coating layer, so the photocatalyst particle. Activity can be maintained. The covering portion covers the third region 10c of the first photocatalyst particle 10 and part or all of the third region 20c of the second photocatalyst particle 20 in addition to the third region 40c of the conductive particle 40. For example, the strength of the photocatalyst layer 70 is increased and the durability is improved. However, in this aspect, since a part of the surface of the photocatalyst particle is covered, the coating layer can be adjusted so that the balance between the maintenance of the photocatalyst particle activity and the strength of the photocatalyst layer can be maintained well. desirable.

In the present invention, an example in which the covering portion exhibits the reverse reaction preventing effect will be described.
In the photocatalyst material of the present invention, hydrogen and oxygen can be generated by decomposing water by irradiation with visible light. At this time, hydrogen and oxygen gas generated by the water splitting reaction in water react with the conductive particles as a catalyst on the surface of the conductive particles, so that a reverse reaction to generate water occurs, and the generated hydrogen In addition, there is a problem that the amount of oxygen decreases. When the conductive particles are metal particles such as gold, the metal particles act as a reverse reaction catalyst and the reverse reaction tends to be promoted. On the other hand, for example, the reverse reaction can be prevented by carrying out water splitting in a reduced pressure state, but a simpler method in practice is preferable. In the present invention, by providing the covering part 60 on the conductive particle 40, hydrogen or oxygen molecules generated by water splitting diffuse to the third region 40 c that is the outer surface of the conductive particle 40, and It has been found that the generation of water accompanying the reverse reaction of hydrogen and oxygen can be prevented. Therefore, a reverse reaction can be effectively prevented with a simple configuration, and a decrease in hydrogen production ability can be suppressed.

In the present invention, an example in which the covering portion 60 has the effect of promoting the generated gas detachment will be described.
The photocatalyst layer 70 according to the present invention includes fine photocatalyst particles (10, 20) and conductive particles 40, and has pores 71 between these particles. In the surface of the photocatalyst layer 70 in contact with water and light, water decomposition occurs and hydrogen gas and oxygen gas are generated. At this time, when hydrogen gas and oxygen gas are not separated from the surface of the photocatalyst layer 70, the amount of gas generation does not increase. Therefore, the hydrophilic covering portion 60 is provided in at least one of the third region 40c of the conductive particles 40, the third region 10c of the first photocatalyst particle 10, and the third region 20c of the second photocatalyst particle 20. Thus, the separation of the hydrophobic hydrogen gas and oxygen gas from the photocatalyst layer 70 is promoted.

An example in which the covering portion 60 has an effect of preventing peeling in the present invention will be described.
The photocatalyst material according to the present invention is exposed to a state in contact with running water or the like for a long period of time. Therefore, it is important that the photocatalyst layer 70 does not peel from the base material 90. In order to give practically sufficient adhesion strength between the photocatalyst layer 70 and the substrate 90, for example, it is conceivable that the photocatalyst layer 70 is baked on the substrate at a high temperature. However, in order to achieve mass production and cost reduction, it is preferable that sufficient adhesion can be ensured even when baking is not performed or low-temperature baking is performed.
In the present invention, in the photocatalyst layer 70, the first and second photocatalyst particles 10 of the conductive particles 40 having the smallest particle diameter and easy to peel off are provided by providing the covering portion 60 on at least a part of the conductive particles 40. , 20 can be increased in strength, and separation of particles can be prevented. The covering portion 60 can be formed using, for example, particles that function as a filler that enhances the adhesion between the photocatalyst layer 70 and the substrate 90.

The covering portion 60 can be formed using, for example, glass frit or inorganic oxide fine particles. As the glass frit, a low melting point glass frit is preferably used. As the inorganic oxide, for example, materials such as silica, alumina, ZrO ₂ and TiO ₂ are preferably used. The average primary particle diameter of the glass frit or the inorganic oxide fine particles is preferably 100 nm or less. By setting the particle size within this range, it is possible to smoothly diffuse water, hydrogen, and oxygen gas into the photocatalyst layer without reducing the photocatalytic activity.

In the present invention, an example in which the covering portion 60 has an antioxidant effect will be described.
When the conductive particles are, for example, a carbon material, the carbon material tends to be easily oxidized. When the carbon material is oxidized, for example, the conductivity is impaired, the carbon material cannot function sufficiently as the conductive particles 40, and the water splitting performance may deteriorate over time. Then, even if it is a case where the material which is easy to oxidize is selected as the electroconductive particle 40 by providing the coating | coated part 60 in at least one part of the electroconductive particle 40 surface, for example, the surface of the electroconductive particle accompanying a photocatalytic reaction, for example Oxidation can be suppressed.

  In the present invention, examples of the state of the covering portion 60 include a continuous layer and a discontinuous island structure. For the purpose of preventing the reverse reaction, it is sufficient that the contact between the hydrogen molecules or oxygen molecules and the conductive particles 40 can be inhibited. For example, a discontinuous island structure may be used. For example, colloidal particles may be supported on the third region 40 c of the conductive particles 40. For the purpose of preventing peeling, the covering portion 60 may be constituted by a dense continuous layer, for example. The thickness can be appropriately selected as long as the water splitting performance is not impaired. In addition, about the coating | coated part 60, it can analyze by the high magnification observation of the torn surface of a photocatalyst material with a transmission electron microscope (TEM).

In the present invention, the covering portion 60 is made of, for example, one kind of hydroxide, oxide or phosphate selected from iron, silicon, chromium, titanium, zirconium, tantalum, niobium, aluminum, magnesium, lanthanum, and cerium. It is preferable to include. More preferred are ferric trioxide (Fe ₂ O ₃ ), silica (SiO ₂ ), zirconium oxide (ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ), cerium oxide (CeO ₂ ), ferric trioxide, zirconium oxide Is more preferable. The thickness t60 of the covering portion 60 is preferably 0.5 nm or more and 50 nm or less, and more preferably 2 nm or more and 10 nm or less, and 2 nm or more and 5 nm or less. In the case where the covering portion is formed of colloidal particles, a single particle film is preferable. Moreover, when forming a coating | coated part with a metal monomer, it is preferable that the thickness shall be less than 10 nm. In addition, a hydrophilic material can be used suitably as a material which comprises a coating | coated part.

  A specific example of the covering portion 60 will be described in more detail with reference to FIGS. 3-5 is typical sectional drawing for demonstrating the photocatalyst material by this invention. As a first example, a photocatalyst material 101 is shown. As shown in FIG. 3, in the photocatalytic material 101, the photocatalytic layer 70 includes a covering portion 60. In this example, the covering portion 60 includes a plurality of colloidal particles 61. In the photocatalyst material 101, a plurality of colloidal particles 61 are arranged in the first and second photocatalyst particles (10, 20) and the third region 40 c that is the outer surface of the conductive particles 40. Here, the “outer surface” means a portion other than the portion (first region 40a, second region 40b) of the surface of the target particle that is in physical contact with the particles contained in the photocatalyst layer 70 other than the target particle. This refers to the portion (third region 40c).

  The “outer surface of the first photocatalyst particle 10” refers to physical contact with particles contained in the photocatalyst layer 70 such as the conductive particles 40 and the second photocatalyst particles 20 among the surfaces of the first photocatalyst particles 10. Say the part other than the part you are doing. The surface of the first photocatalytic particle 10 has a first region 10a, a second region 10b, and a third region 10c. In the first region 10a, the first photocatalyst particle 10 and the second photocatalyst particle 20 are in contact with each other. In the second region 10b, the first photocatalyst particles 10 and the conductive particles 40 are in contact with each other. In the first photocatalyst particle 10, the third region 10c is a region other than the first region 10a and the second region 10b. The third region 10 c corresponds to the outer surface of the first photocatalyst particle 10.

  The “outer surface of the second photocatalyst particle 20” refers to physical contact with particles contained in the photocatalyst layer 70 such as the conductive particles 40 and the first photocatalyst particle 10 among the surfaces of the second photocatalyst particle 20. Say the part other than the part you are doing. The surface of the second photocatalytic particle 20 has a first region 20a, a second region 20b, and a third region 20c. In the 1st field 20a, the 2nd photocatalyst particle 20 and the 1st photocatalyst particle 10 contact. In the second region 20b, the second photocatalyst particles 20 and the conductive particles 40 are in contact with each other. In the second photocatalyst particle 20, the third region 20c is a region other than the first region 20a and the second region 20b. The third region 20 c corresponds to the outer surface of the second photocatalyst particle 20.

  In the photocatalyst material 101, a plurality of colloidal particles 61 are disposed as the covering portion 60 on the outer surface (third region 40c) of the conductive particles 40, so that the reverse reaction and oxidation of the conductive particles 40 are effective. Can be suppressed. Further, when hydrophilic particles are used as the colloidal particles 61, gas detachment can be promoted and the hydrogen generation ability is improved. In the photocatalyst material 101, the strength of the photocatalyst layer 70 is increased and the durability is improved.

  As a method for forming the covering portion 60 including the plurality of colloidal particles 61, for example, after forming a layer including the first photocatalyst particle 10, the second photocatalyst particle 20, and the conductive particles 40 on the substrate, the covering portion 60 is formed. A method of adsorbing the dispersion containing the colloidal particles 61 to the surface of the layer can be used. Or you may use the method of depositing a colloid directly on the surface of the electroconductive particle 40 by a chemical reduction method, a photoreduction method, etc. FIG. Alternatively, a method may be used in which a layer including the first photocatalyst particle 10 and the second photocatalyst particle 20, the conductive particle 40, and the colloidal particle 61 that becomes the covering portion 60 is formed on the substrate 90. In this case, by reducing the blending ratio (weight ratio) of each particle in the order of photocatalyst particles, colloid particles, and conductive particles, or in the order of photocatalyst particles, conductive particles, and colloid particles, for example, a highly efficient photocatalyst. It is possible to achieve both characteristics and suppression of reverse reaction. Alternatively, the primary particle diameter may be decreased in the order of photocatalyst particles, colloidal particles, and conductive particles, or in the order of photocatalyst particles, conductive particles, and colloidal particles.

  A photocatalyst material 102 is shown as a second example. As shown in FIG. 4, in the photocatalytic material 102, the photocatalytic layer 70 includes a covering portion 60. The covering portion 60 is made of, for example, a continuous covering layer 62. The coating layer 62 is disposed so as to cover the outer surfaces (third regions 10c, 20c, 40c) of the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40, respectively. In this example, the covering layer 62 has a substantially continuous layer structure, but may have a part of discontinuous portions. The covering layer 62 can effectively suppress, for example, reverse reaction and oxidation of the conductive particles 40. Further, by making the coating portion hydrophilic, it is possible to promote separation of the generated gas. In the photocatalyst material 102, the strength of the photocatalyst layer 70 is increased and the durability is improved. The coating layer 62 may be any of an amorphous phase, a crystal phase, and a hydroxide phase.

  As a method for forming the coating layer 62, for example, a raw material containing a monomer, oligomer or polymer metal is adsorbed on the surfaces of the conductive particles 40 and / or the photocatalyst particles 10 and 20, and in some cases by heating or chemical reaction. A method of polymerizing raw materials on the surfaces of the conductive particles 40 and / or the photocatalyst particles 10 and 20 can be used. Thereby, it is possible to form a coating layer. The coating layer can also be formed by a dry film forming method (sputtering method, vapor deposition method, CVD method, atomic layer deposition method, etc.), chemical reduction method, photoreduction method, or the like.

  A photocatalyst material 103 is shown as a third example. As shown in FIG. 5, in the photocatalytic material 103, the photocatalytic layer 70 includes a covering portion 60. The covering portion 60 includes a covering layer 63. The coating layer 63 is disposed only on the outer surface (third region 40 c) of the conductive particles 40. For this reason, a reverse reaction, oxidation of the electroconductive particle 40, etc. can be suppressed, without inhibiting the water splitting activity of the 1st and 2nd photocatalyst particles 10 and 20. Further, by making the coating portion hydrophilic, it is possible to promote separation of the generated gas. Furthermore, the adhesion between the conductive particles 40 and the first and second photocatalyst particles 10 and 20 can be increased, and the strength of the photocatalyst layer 70 can be increased.

  As a method for forming the coating layer 63, for example, raw material molecules containing a monomer, oligomer or polymer metal are adsorbed on the surface of the conductive particles 40, and in some cases, the raw material is formed on the surface of the conductive particles 40 by heating or chemical reaction. A method of polymerizing molecules can be used. Thereby, the coating layer 63 can be formed. Also, the coating layer 63 can be formed by a chemical reduction method, a photoreduction method, or the like using a molecule containing a monomer, oligomer, or polymer metal as a raw material. In addition, a functional group capable of forming an electrostatic interaction such as a metal-carboxylic acid bond or a specifically strong chemical bond such as a metal-sulfur bond is formed on the conductive particle 40 with a metal. You may introduce | transduce into the raw material molecule | numerator containing. Thereby, the coating layer 63 can be selectively disposed on the surface of the conductive particles 40.

Intermediate Layer According to a preferred embodiment of the present invention, as shown in FIGS. 6 and 7, the photocatalyst material 100 may further include an intermediate layer 80 between the base material 90 and the photocatalyst layer 70. The intermediate layer 80 is disposed between the base material 90 and the photocatalyst layer 70 and is connected to each of the base material 90 and the photocatalyst layer 70. Thereby, for example, the adhesion between the substrate 90 and the photocatalyst layer 70 can be improved. As a material used for the intermediate | middle layer 80, the electroconductive particle 40 and the nonelectroconductive particle with a small aspect-ratio mentioned later are mentioned, for example. The intermediate layer 80 formed using the conductive particles 40 is excellent in water photolysis performance. The intermediate layer 80 formed using non-conductive particles having a small aspect ratio functions as a binder, and the photocatalyst layer 70 can be firmly adhered to the base material 90. When the photocatalyst material 100 includes the intermediate layer 80, the thickness of the intermediate layer 80 can be evaluated by observing the fracture surface of the layer with a scanning electron microscope.

Other Particles According to a preferred embodiment of the present invention, the photocatalyst layer 70 of the photocatalyst material 100 may further include other particles other than the photocatalyst particles (10, 20) and the conductive particles 40.

  In the present invention, the other particles are preferably particles that do not cover the surface of the photocatalyst particles (10, 20). Thereby, the fall of the photocatalytic activity of the photocatalyst material 100 can be suppressed. Preferable examples of other particles include particles having a small aspect ratio. Further, as other particles, it is preferable to use particles having a small absorption in the visible light region. Thereby, it can suppress that the light absorption of a photocatalyst particle (10, 20) is inhibited.

In the present invention, when water is photodecomposed using the first photocatalyst particle 10 and the second photocatalyst particle 20, a promoter can be supported on the surface of the photocatalyst particle. Thereby, the reduction and oxidation reaction of water is promoted, and the generation efficiency of hydrogen and oxygen is improved. The cocatalyst is provided, for example, in a part of the third region 10 c of the first photocatalyst particle 10 and / or the third region 20 c of the second photocatalyst particle 20.

  The cocatalyst for the first photocatalyst particle 10 is one or more selected from the group consisting of metal particles such as platinum, ruthenium, iridium and rhodium, or the group consisting of oxide particles such as ruthenium oxide and nickel oxide. One or more selected, or a mixture of these metal particles or oxide particles, or a composite hydroxide or composite oxide containing rhodium and chromium can be preferably used. More preferably, platinum, ruthenium metal particles, or a composite hydroxide or composite oxide containing rhodium and chromium can be used. By supporting this promoter on the surface of the first photocatalyst particle 10 in the form of particles, it becomes possible to reduce the activation energy in the reduction reaction of water, so that hydrogen can be generated promptly.

  In the present invention, it is also possible to cover at least a part of a portion of the promoter surface of the first photocatalyst particle 10 other than the portion in physical contact with the first photocatalyst particle 10 with another layer. is there. Thereby, the water molecule production | generation by the reverse reaction of the hydrogen and oxygen molecule on the promoter surface of the 1st photocatalyst particle 10 can be suppressed. This another layer preferably contains an amorphous oxide or hydroxide containing at least one selected from silicon, chromium, titanium, zirconium, tantalum, niobium, aluminum and magnesium, an oxide crystal, or a phosphate. . The material constituting another layer covering the promoter is preferably amorphous. Thereby, diffusion of protons and water molecules to the promoter surface can be suppressed. Further, it is possible to suppress hydrogen gas and oxygen gas from entering the promoter. The thickness of the other layer is preferably 1 nm or more and 50 nm or less, and more preferably 2 nm or more and 20 nm or less.

  As the cocatalyst of the second photocatalyst particle 20, one or more selected from the group consisting of metals such as Mn, Fe, Co, Ir, Ru, Ni, or a metal oxide obtained by mixing these metals, Particles made of metal hydroxide or metal phosphate can be preferably used. More preferably, metal oxide particles or metal hydroxide particles containing one or more selected from Mn, Co, and Ru can be used.

  The average primary particle size of these promoters is preferably less than 10 nm, more preferably 5 nm or less. By reducing the average primary particle size, it can function efficiently as an active point of hydrogen and oxygen generation reaction, and can exhibit a sufficient function as a promoter. When the average primary particle size of the cocatalyst is 10 nm or more, the number of active sites per supported weight decreases as water reduction or oxidation reaction sites, so that efficient water decomposition may be suppressed.

  Preferred examples of the cocatalyst loading method include an impregnation method and an adsorption method. The impregnation method and the adsorption method are methods in which the photocatalyst particles (10, 20) are dispersed in a solution in which the cocatalyst precursor is dissolved, and the cocatalyst precursor is adsorbed on the surface of the photocatalyst particles (10, 20). Examples of the cocatalyst precursor include chlorides, nitrates, and ammine salts of metals such as platinum, ruthenium, iridium, rhodium, and nickel.

  In addition, when the promoter precursor is supported on the surface of the photocatalyst particles 10, the activity is increased by making the metal state. Therefore, it is preferable to reduce the cocatalyst precursor on the surface of the photocatalyst particle 10 and deposit it in a state containing a metal. As a method for reducing the cocatalyst precursor, a photoreduction method, a chemical reduction method, or the like is preferably used. The photoreduction method is a method in which the promoter precursor adsorbed on the photocatalyst particles 10 is reduced by excited electrons generated in the photocatalyst particles 10 by irradiation of the photocatalyst particles with ultraviolet light or visible light. The chemical reduction method is a method of reducing the cocatalyst precursor in a hydrogen gas stream at 400 ° C. or lower, preferably 300 ° C. or lower. The cocatalyst supported by such a method is in the form of particles. Since the cocatalyst is supported on the surface of the first photocatalyst particle 10, the activation energy in the reduction reaction of water can be reduced, so that hydrogen can be generated promptly.

  The amount of the cocatalyst supported on the surface of the photocatalyst particle can be appropriately determined within a range in which the irradiation light to the photocatalyst particle is not shielded by the presence of the cocatalyst. The amount of cocatalyst is preferably small.

Specific Structure of Photocatalyst Material The structure of the photocatalyst material according to the present invention will be described with reference to specific examples of Embodiments 1 to 6 below. The photocatalyst material according to the present invention is not limited by these embodiments.

(Embodiment 1)
As a specific example of the photocatalyst material according to the present invention, the photocatalyst material 100 will be described with reference to FIG. 1 again. In the photocatalyst material 100, the first photocatalyst particles 10 and the second photocatalyst particles 20 are approximately on the surface of the base material 90 in the plane direction (XY plane) and the thickness direction (Z direction) of the photocatalyst material 100. Alternatingly arranged. Further, the first photocatalyst particles 10 and the second photocatalyst particles 20 are uniformly and densely arranged throughout the photocatalyst layer 70. Then, the first photocatalyst particles 10 and the second photocatalyst particles 20 that are arranged almost alternately and densely throughout the photocatalyst layer 70 as described above are electrically conductive so as to come into contact with these particles. The particles 40 are arranged with high density and uniformity. In Embodiment 1, the 1st photocatalyst particle 10 and this electroconductive particle 40 are contacting in the arbitrary site | parts (1st area | region 40a) of the surface of the one electroconductive particle 40 which exists in the form of a primary particle. The second photocatalyst particle 20 and the conductive particle 40 are in contact with each other on the surface of the same conductive particle 40 (second region 40b). That is, the first photocatalyst particle 10 and the second photocatalyst particle 20 are in contact via the same conductive particle 40. The photocatalyst layer 70 has pores 71. The pore 71 is disposed between the first photocatalyst particle 10, the second photocatalyst particle 20, and the conductive particle 40. The pores 71 can ensure contact between water, hydrogen, and oxygen gas and the particles 10, 20, and 40. Therefore, even if the photocatalyst layer 70 has a layer structure, a relatively high water splitting performance can be achieved.

  In the first embodiment, since the first photocatalyst particles 10 and the second photocatalyst particles 20 are alternately arranged in both the planar direction and the thickness direction, the photocatalyst layer base material 90 has visible light permeability. In some cases, light can be irradiated from any direction. Therefore, on the entire surface of the photocatalyst layer 70, the first photocatalyst particles 10 and the second photocatalyst particles 20 can efficiently absorb light according to the respective light absorption characteristics. Further, the second photocatalyst particle 20 disposed in the innermost layer of the outermost layer is the light that has been transmitted without being absorbed by the first photocatalyst particle 10 or the second photocatalyst particle 20 disposed in the outermost layer. Alternatively, it can be absorbed by the first photocatalyst particles 10. In addition, the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40 are arranged at high density and uniformly over the entire photocatalyst layer 70. Therefore, the charge recombination reaction between the photoexcited holes generated by the first photocatalyst particles and the photoexcited electrons generated by the second photocatalyst particles can occur promptly or with high efficiency via the conductive particles 40. As a result, highly efficient photolysis of water becomes possible.

  On the other hand, in the conventional mode in which the first photocatalyst particles 10 and the second photocatalyst particles 20 are dispersed in a dispersion medium, there is a problem in realizing an efficient water splitting reaction. For example, it is always necessary to input external energy such as stirring and circulation to uniformly disperse the photocatalyst particles in water. Therefore, the method using a dispersion medium is not suitable for an efficient photocatalytic water splitting reaction device.

  A layer structure in which the first photocatalyst particles 10 and the second photocatalyst particles 20 are fixed on the same metal sheet has also been proposed. In this case, in order to form a good connection between the photocatalyst particles and the metal sheet layer, in addition to the photocatalyst particle layer formation, a multi-step process such as metal vapor deposition, metal sheet layer formation by sputtering or the like is essential. there were. Furthermore, since the dry film forming method is used, the layer structure in which the photocatalyst particles (10, 20) are immobilized on the same metal sheet is unsuitable for producing a large-area water-splitting photocatalyst material.

  In the present invention, the first and second photocatalyst particles 10 and 20 and the conductive particles 40 are arranged as described above to form the layer structure of the photocatalyst layer, so that the water decomposition performance is as high as practically effective. The present inventors have found that it is obtained for the first time.

(Embodiment 2)
As a specific example of the photocatalyst material according to the present invention, a photocatalyst material 110 will be described with reference to FIG. In the photocatalyst material 110, the intermediate layer 80 is provided on the surface of the substrate 90, and the photocatalyst layer 70 is provided thereon. The intermediate layer 80 includes conductive particles 40.

  In the second embodiment, when light such as sunlight is incident from the upper surface side of the photocatalyst layer 70, the first photocatalyst particles 10 and / or the second photocatalyst particles 20 that are initially present on the outermost layer of the photocatalyst layer 70 are used. Incident light will hit. Therefore, efficient light absorption by the photocatalyst particles (10, 20) becomes possible. Furthermore, the first photocatalyst particles 10 and the second photocatalyst particles 20 are electrically connected via the conductive particles 40 included in the photocatalyst layer 70 or the conductive particles 40 included in the intermediate layer 80, respectively. Therefore, the charge recombination reaction is promoted, and as a result, efficient photolysis of water becomes possible.

  In the second embodiment, the example in which the intermediate layer 80 includes the conductive particles 40 has been described. However, the intermediate layer 80 is, for example, a non-conductive particle having a small aspect ratio, for example, a non-conductive material such as a glass frit or an inorganic oxide. May contain fine particles. In this case, the intermediate layer 80 allows the photocatalyst layer 70 to be firmly adhered to the base material 90. The intermediate layer 80 may include particles obtained by combining a plurality of these particles.

(Embodiment 3)
As a specific example of the photocatalyst material according to the present invention, a photocatalyst material 120 will be described with reference to FIG. In the photocatalyst material 120, the photocatalyst layer 70 and the intermediate layer 80 in the first embodiment further include the conductive wire 50. The conductive wire 50 is a particle having a large aspect ratio, for example, having a rod-like or needle-like form.

  In the third embodiment, for example, the conductive wire 50 having an appropriate aspect ratio of 5 to 1000 is used. Therefore, compared with the case where isotropic conductive particles are used, the first photocatalyst particles 10 and the second photocatalyst particles 20 are simultaneously formed with one conductive wire or a plurality of electrically connected conductive wires. Probability of being connected increases. Therefore, the charge recombination reaction is promoted, and as a result, efficient photolysis of water becomes possible. In addition, the adhesion between the photocatalyst particles 10 and 20 and the conductive particles 40 and the adhesion between these particles (10, 20, 40) and the substrate 90 can be further enhanced.

  In Embodiment 3, for example, conductive particles and / or non-conductive particles having an aspect ratio as small as about 1 to 3 may be further included together with the conductive wire. Thereby, the particles having a small aspect ratio can function as a filler. As a result, the mechanical and / or electrical properties of the photocatalyst material 120 can be improved. When non-conductive particles are used as the particles having a small aspect ratio, it is preferable to select particles having small absorption in the visible light region. Thereby, it is suppressed that the light absorption of a photocatalyst particle (10, 20) is inhibited.

(Embodiment 4)
As a specific example of the photocatalyst material according to the present invention, a photocatalyst material 130 will be described with reference to FIG. In the photocatalyst material 130, the photocatalyst layer 70 is provided on the surface of the base material 90. In this example, the photocatalytic layer 70 includes three layers. A layer of the first photocatalyst particles 10 is provided on the surface of the substrate 90. A layer of second photocatalyst particles 20 is further provided on the layer of first photocatalyst particles 10. Furthermore, a layer of conductive particles 40 is disposed between the layer of first photocatalyst particles 10 and the layer of second photocatalyst particles 20. The first photocatalyst particles 10 and the second photocatalyst particles 20 are electrically connected by the layer of the conductive particles 40.

  In Embodiment 4, it can be set as the efficient light absorption system in which the light absorption characteristic of the photocatalyst particle (10, 20) was considered. Specifically, the photocatalyst is established so that the relationship of λ1> λ2 is established between the light absorption edge wavelength (λ1) of the first photocatalyst particle 10 and the light absorption edge wavelength (λ2) of the second photocatalyst particle 20. Select particles. In this case, since the layer of the second photocatalyst particle 20 is provided on the outermost surface of the photocatalyst material 130, the layer of the second photocatalyst particle 20 can first absorb light on the short wavelength side. Next, the first photocatalyst particle 10 layer provided below the second photocatalyst particle 20 layer absorbs the light on the long wavelength side that is transmitted without being absorbed by the second photocatalyst particle 20 layer. It becomes possible. Thereby, it can avoid or suppress that the light of the same wavelength is absorbed by different photocatalyst particles, and the efficient light absorption according to the light absorption characteristic of each photocatalyst particle is attained.

As the photocatalyst material 130, the example of the photocatalyst layer 70 in which the layer of the first photocatalyst particle 10 and the layer of the second photocatalyst particle 20 are stacked in this order on the surface of the base material 90 has been described. The layer of the second photocatalyst particle 20 and the layer of the first photocatalyst particle 10 may be laminated in this order. In this case, the photocatalyst particles are arranged so that the relationship of λ1 <λ2 is established between the light absorption edge wavelength (λ1) of the first photocatalyst particle 10 and the light absorption edge wavelength (λ2) of the second photocatalyst particle 20. It is preferable to select.
In the photocatalyst material 130, an intermediate layer 80 may be provided between the photocatalyst layer 70 and the base material 90. As the intermediate layer 80, those described in the photocatalyst material 110 and the photocatalyst material 120 can be used.

(Embodiment 5)
As a specific example of the photocatalyst material according to the present invention, a photocatalyst material 104 will be described with reference to FIG. The photocatalyst material 104 differs from the first embodiment in the form of the conductive particles 40. That is, in Embodiment 5, as for the electroconductive particle 40, the several primary particle or the one or several secondary particle has joined, for example. In the photocatalyst material 104, for example, a plurality of particles are chemically bonded by heating or the like. Thereby, these particles (10, 20, 40) are connected in a network, and a uniform and dense matrix structure is formed. The photocatalyst material 104 has the same configuration as the photocatalyst material 100 except that the shape of the conductive particles 40 is different from that of the photocatalyst material 100. In the photocatalyst material 104, a relatively high water splitting performance can be achieved as in the photocatalyst material 100. Further, in the photocatalyst material 104, the adhesion between the photocatalyst layer 70 and the substrate 90 can be improved.

(Embodiment 6)
As a specific example of the photocatalyst material according to the present invention, a photocatalyst material 105 will be described with reference to FIG. The photocatalyst material 105 is different from the first embodiment in the form of the conductive particles 40. That is, in Embodiment 5, the conductive particles 40 constitute so-called secondary particles in which primary particles are aggregated, associated or aggregated. Thus, even when the conductive particles 40 are aggregated, the effects of the present invention are exhibited as long as the first photocatalyst particles 10 and the second photocatalyst particles 20 are electrically connected. The conductive particles 40 may be not only primary particles but also aggregates.

Production Method of Photocatalyst Material As a production method of the photocatalyst material (100 to 105, 110, 120, 130) according to the present invention, the first photocatalyst particle 10, the second photocatalyst particle 20, A method that can fix the photocatalyst layer 70 including the conductive particles 40 that electrically connect the first photocatalyst particle 10 and the second photocatalyst particle 20 to form the above structure can be used.

  According to a preferred embodiment of the present invention, the photocatalyst materials 100 to 105 according to the present invention are produced by mixing the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40 and performing wet dispersion. A method in which the liquid is applied to the substrate 90 and dried can be used. In addition, as a dispersion liquid, a paste-form thing can be used, for example.

  For example, a method of adding the conductive particles 40 separately afterwards may be used. Specifically, according to another preferred embodiment of the present invention, in the method for producing the photocatalyst materials 100 to 105 according to the present invention, the first photocatalyst particles 10 and the second photocatalyst particles 20 are mixed and wet dispersed. The dispersion is applied to the substrate 90 and dried to obtain a photocatalytic film. Further, a dispersion liquid in which the conductive particles 40 are wet-dispersed is dropped onto the photocatalyst film. At this time, with drying, for example, the conductive particles 40 move to the grain boundaries 10 and 20 of the first and second photocatalyst particles. Thereby, the photocatalyst materials 100 to 105 can be obtained.

  According to another preferred embodiment of the present invention, in the method for producing the photocatalyst materials 100 to 105 according to the present invention, the conductive particles 40 are previously supported on the surface of either the first photocatalyst particle 10 or the second photocatalyst particle 20. Then, the first photocatalyst particle 10 or the second photocatalyst particle 20 carrying the conductive particles 40, and the other photocatalyst particle (the first or second photocatalyst particle 10, 20) is applied to the base material 90 and dried. At this time, the method for supporting the conductive particles 40 on the surface of either the first photocatalyst particle 10 or the second photocatalyst particle 20 in advance is the same as the method for supporting the cocatalyst on these photocatalyst particles (impregnation). Method, adsorption method, photoreduction method, chemical precipitation method, etc.).

  In the above two embodiments, glaze fine particles may be further added to the dispersion. By heating the dispersion liquid to which the glaze fine particles are added, for example, to 300 ° C. or less, each glaze fine particle adheres to the surface of the substrate 90. Therefore, the adhesiveness of the photocatalyst layer 70 to the base material 90 can be improved. Moreover, since the glaze fine particles do not completely cover the surface of the photocatalyst particles (10, 20), it is possible to suppress a decrease in the photocatalytic activity of the photocatalyst material.

  In the above two embodiments, for example, the intermediate layer 80 may be formed before applying the dispersion containing the photocatalyst particles. The intermediate layer 80 can be formed by, for example, applying a dispersion liquid containing the conductive particles 40 or non-conductive particles having a small aspect ratio to the substrate 90. After forming the intermediate layer 80, the photocatalyst layer 70 may be formed by applying a dispersion liquid containing photocatalyst particles. The photocatalyst layer 70 may be formed after the intermediate layer 80 is formed and then dried. Alternatively, after forming a photocatalyst film containing the first photocatalyst particles, the second photocatalyst particles and the conductive particles on the first substrate, a paste containing conductive particles, for example, is further applied on the photocatalyst film. Then, it is dried and fired to further form a conductive particle film. Then, the 2nd base material provided with adhesion layers, such as a carbon tape, is pressed against this conductive particle film, and the 1st base material is removed. Thus, a photocatalyst material in which a photocatalyst film is formed on the second substrate via the conductive particle film (intermediate layer) can be obtained.

  According to still another preferred aspect of the present invention, in the method for producing the photocatalyst material 130 according to the present invention, a dispersion in which the first photocatalyst particles 10 are wet dispersed, and a dispersion in which the conductive particles 40 are wet dispersed. A dispersion liquid in which the second photocatalyst particles 20 are wet-dispersed is prepared independently. Then, these dispersions may be alternately applied to the substrate 90 by a so-called “alternate adsorption method” and dried. Thereby, the photocatalyst layer 70 in which the first photocatalyst particles 10, the conductive particles 40, and the second photocatalyst particles 20 are alternately stacked on the surface of the base material 90 in this order, for example, is formed. As a method of applying each dispersion liquid alternately, for example, a method of immersing the substrate 90 in each dispersion liquid can be used.

  In this embodiment, a dispersion liquid obtained by wet-dispersing glaze fine particles may be further prepared. For example, the glaze dispersion liquid is first applied to the substrate 90 and dried, and the glaze fine particles, the first photocatalyst particles 10, the conductive particles 40, and the second photocatalyst particles 20 are, for example, in this order on the surface of the substrate 90. You may form the photocatalyst layer 70 laminated | stacked alternately. By forming a layer of glaze fine particles on the surface of the base material 90, the adhesion of the photocatalyst layer 70 to the base material 90 can be improved.

  In the present invention, as a method of dispersing the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40 in the liquid medium, the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40 are used. A method of adsorbing a solvent or dispersant such as water or an organic solvent on the surface of each particle can be preferably used. Thereby, it is possible to realize a state in which each particle is in a form close to the primary particle and stably mixed. That is, aggregation of the first photocatalyst particles 10, the second photocatalyst particles 20, or the conductive particles 40 can be suppressed. Therefore, in the photocatalyst layer 70, the first photocatalyst particle 10 and the second photocatalyst particle 20 can exist at a short distance via the conductive particle 40. Therefore, the water splitting reaction is promoted, and the hydrogen generation efficiency can be increased.

  In the present invention, as a wet dispersion method, a mechanical dispersion method such as ultrasonic irradiation, ball mill, or bead mill can be preferably used.

  In the present invention, a solvent capable of dispersing the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40 can be used as the liquid medium. According to a preferred embodiment of the present invention, an organic solvent such as water or ethanol, or an organic vehicle solvent such as α-terpineol can be used as such a solvent. Moreover, in order to improve the dispersibility in the solvent of the 1st photocatalyst particle 10, the 2nd photocatalyst particle 20, and the electroconductive particle 40, you may add a dispersing agent to a solvent.

  In the present invention, a spin coating method, a dip coating method, a spray method, a doctor blade method, an electrophoresis method, a screen printing method, or the like can be preferably used as a method for applying the dispersion liquid to the substrate 90. Further, the coating method can be appropriately selected according to the shape and type of the substrate 90.

  In the present invention, it is possible to calculate a preferable range of the thickness of the photocatalyst layer 70 in consideration of the light absorption coefficient of the photocatalyst material used. The thickness of the photocatalyst layer 70 may be set in the range of 0.1 to 50 μm, for example.

  In order to achieve the target layer thickness, a method for forming the photocatalyst layer 70 can be selected as appropriate. For example, when obtaining the photocatalyst layer 70 having a thickness of 1 μm or less, it is preferable to use a spin coating method, a dip coating method, a spray method, or the like. When obtaining the photocatalyst layer 70 having a thickness of 1 μm or more, it is preferable to use a screen printing method, a doctor blade method, an electrophoresis method or the like.

  According to a preferred aspect of the present invention, a method of dispersing the first photocatalyst particles 10 and the second photocatalyst particles 20 in a liquid medium is performed by, for example, combining the first photocatalyst particles 10 and the second photocatalyst particles 20 respectively. A step of dispersing in a solution containing a polymer having different charges such as an anionic polymer and a cationic polymer to make it close to a monodispersed state dispersed in a primary particle state. Thereafter, the obtained dispersion liquid is mixed, and the first photocatalyst particle 10 and the second photocatalyst particle 20 are each caused by Coulomb interaction due to different charges of the polymer adsorbed on the surface of each photocatalyst particle (10, 20). Spontaneously adsorbing each other, it becomes possible to approach or contact. For example, the first photocatalyst particles 10 are dispersed in a solution containing an anionic polymer, and the second photocatalyst particles 20 are dispersed in a solution containing a cationic polymer. Then, by mixing these dispersions, it becomes possible to bring the primary particles into close contact or contact with each other with high density. Thereafter, the primary particles are heated or fired in a state where the primary particles are close to or in close contact with each other at a high density, and the polymer is removed, thereby realizing a highly active state as a photocatalyst material for visible light responsive water splitting.

  In the present invention, the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40 are fixed to the substrate 90 by drying, preferably drying and firing, a dispersion containing these. The The firing temperature is equal to or higher than the thermal decomposition temperature of a solvent, a dispersant, and the like, and further, the base material 90 and the first photocatalyst particles 10, the second photocatalyst particles 20 and the conductive particles 40, or the conductive particles 40 and the first. The photocatalyst particles 10 and the second photocatalyst particles 20, or the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40 are preferably at a temperature that can promote firing. Specifically, it is 100 ° C. or higher and 700 ° C. or lower, more preferably 200 ° C. or higher and 600 ° C. or lower, and further preferably 300 ° C. or higher and 400 ° C. or lower. By firing at a temperature in this range, it is possible to obtain a long-term stable visible light responsive photocatalyst for water splitting, which has high adhesion to the substrate 90 and high adhesion between particles (10, 20, 40). It becomes possible. The firing atmosphere may be any atmosphere of air, nitrogen, and reducing gas (ammonia, hydrogen). Preferably, it is air or nitrogen atmosphere. Thereby, the loss | disappearance of the binder at the time of baking occurs efficiently. In addition, the firing in a nitrogen atmosphere can suppress the oxidation of the conductive particles. Therefore, the electroconductive fall of electroconductive particle can be suppressed.

(Mixing ratio)
In the method for producing a photocatalyst material according to the present invention, the mixing ratio of the first photocatalyst particles and the second photocatalyst particles is, as a weight ratio, the first photocatalyst particles: second photocatalyst particles = 10: 90 to 90:10. It is preferable that the ratio is 20:80 to 80:20. By mixing in this range, the charge recombination reaction at the particle interface can be promoted. As a result, the water splitting efficiency of the photocatalyst material can be increased.

Water-Splitting Photocatalyst Module A water-splitting photocatalyst module according to the present invention includes the above-described photocatalyst material. According to a preferred aspect of the present invention, the photocatalyst module for water splitting according to the present invention has a generally transparent light incident surface, and has a structure in which light is incident on a photocatalyst material installed inside the module. Moreover, it has the sealing panel shape which can enclose water so that a photocatalyst material can always contact with water. Further, according to a more preferred aspect of the present invention, the photocatalyst module for water splitting according to the present invention further has a mechanism such as a water passage hole that can gradually supply additional water that decreases as the water splitting reaction proceeds. Is preferred. By using the water-splitting photocatalyst module having such a configuration, it is possible to produce hydrogen that can be used practically.

Hydrogen production system The hydrogen production system according to the present invention includes the photocatalyst module for water splitting. According to a preferred aspect of the present invention, a hydrogen production system according to the present invention comprises a water supply device, a filtration device for removing impurities in water to some extent, a water splitting photocatalyst module, a hydrogen separation device, and a hydrogen storage device. It is. By setting it as the hydrogen production system of such a structure, it becomes possible to implement | achieve the system which can manufacture hydrogen practically from sunlight and water which are renewable energy.

  The following examples further illustrate the present invention. The present invention is not limited to these examples.

The first photocatalyst particles, second photocatalyst particles, and conductive particles used as the raw material will be described.

Production of first photocatalyst particles
Preparation of the first photocatalyst particle 1-1 (3% Rh-doped SrTiO ₃ particle)
3% Rh-doped SrTiO ₃ (SrTi _0.97 Rh _0.03 O ₃ ) particles were prepared by solid phase method. Specifically, SrCO ₃ (Wako Pure Chemical, 99.9%), TiO ₂ (High Purity Chemical Laboratory, 99.99%), and Rh ₂ O ₃ (Wako Pure Chemical) were added at a molar ratio of 1.05: 0.97: 0.03. The mixture was placed in an alumina mortar at a ratio, and methanol was added, followed by mixing for 2 hours. Next, the obtained mixture was put in an alumina crucible, calcined at 900 ° C. for 1 hour, and then calcined at 1050 ° C. for 10 hours. After firing, the fired body was allowed to cool to room temperature and then crushed to produce a powder composed of 3% Rh-doped SrTiO ₃ (SrTi _0.97 Rh _0.03 O ₃ ) particles.

First photocatalyst particles 1-2 (4% La and 4% Rh-doped SrTiO ₃ particles) Preparation strontium carbonate powder (manufactured by Kanto Chemical Co., purity 99.9%, 1 hour calcined powder 200 ° C. in advance) and rutile First, SrTiO ₃ powder is prepared by mixing titanium powder (manufactured by Kanto Chemical Co., Ltd., purity 99.0%) with a mortar so that Sr: Ti = 1.05: 1 (molar ratio) and firing at 1150 ° C. for 10 hours. Got. Further, the obtained SrTiO ₃ powder and lanthanum oxide so that Sr: La = 0.96: 0.04 (molar ratio) and Ti: Rh = 0.96: 0.04 (molar ratio) are obtained. The powder and rhodium oxide (Rh ₂ O ₃ , purity 99.9%) were mixed in ethanol, and the dried powder was calcined at 1100 ° C. for 6 hours, so that 4% La and 4% Rh-doped SrTiO ₃ A powder composed of (Sr _0.96 La _0.04 Ti _0.96 Rh _0.04 O ₃ ) particles was prepared. In addition, as the lanthanum oxide powder (La ₂ O ₃ ), a powder made by Kanto Chemical Co., Ltd. having a purity of 99.99% and calcined at 1000 ° C. for 10 hours in advance was used.

(Average primary particle size)
3% Rh-doped SrTiO ₃ particles by SEM observation (first photocatalyst particles 1-1), and calculates an average primary particle size of 4% La and 4% Rh-doped SrTiO ₃ particles (the first photocatalyst particles 1-2) did. Specifically, an average value by circular approximation of 50 crystal particles when observed at a magnification of 40000 times by SEM (manufactured by Hitachi, Ltd., “S-4100”) was defined as the primary particle diameter. As a result, the average primary particle sizes of 3% Rh-doped SrTiO ₃ particles and 4% La and 4% Rh-doped SrTiO ₃ particles were about 500 nm and about 300 nm, respectively.

(Band structure)
The band positions of 3% Rh-doped SrTiO ₃ particles and 4% La and 4% Rh-doped SrTiO ₃ particles are considered as follows with reference to Wang et al., J. Catal. 305-315, 328 (2015). It was.
Upper end of valence band: -6.6eV (vs. vacuum level)
Bottom of conduction band: -4.1eV (vs. vacuum level)
Note that the top of the valence band in 3% Rh-doped SrTiO ₃ particles and 4% La and 4% Rh-doped SrTiO ₃ particles is the donor orbital derived from the doped Rh ³⁺ generated in the band gap of SrTiO3. It is thought that it originates from the upper end.

Production of second photocatalytic particles
Preparation of second photocatalyst particles 2-1 (CoOx-supported BiVO ₄ particles)
BiVO ₄ particles carrying CoO _x were prepared by a liquid solid phase method. Specifically, first, K ₂ CO ₃ (manufactured by Kanto Chemical Co., 99.5%) and V ₂ O ₅ (manufactured by Wako Pure Chemical Industries, 99.0%) are mixed to make K: V = 3.03: 5 (mol ratio). The mixture was placed in a mortar and ethanol (10 mL) was added and mixed for 30 minutes. Next, the obtained mixture was put in a magnetic crucible and baked in an electric furnace at 450 ° C. for 5 hours in the atmosphere. After firing, the fired body was allowed to cool to room temperature and then crushed.

Put the resulting powder in a 300 mL Erlenmeyer flask containing 100 ml of water and Bi (NO ₃ ) ₃ · 5H ₂ O (Wako, 99.9%) (Bi: V = 1: 1) at 70 ° C. for 10 hours. The mixture was stirred at 1500 rpm using a stir bar. The obtained precipitate was collected by suction filtration and washed with water, and then dried at 60 ° C. for 12 hours in a drier to obtain BiVO ₄ powder.

Put 0.5 g of the obtained BiVO ₄ powder in a magnetic crucible, and put Co (NO ₃ ) ₂ (Wako, 99.5%) in the magnetic crucible so that CoO is 0.5 wt% as a raw material for the promoter. A small amount was added. The BiVO ₄ powder was sufficiently suspended by ultrasonic waves and then evaporated to dryness in a hot water bath. Finally, it was fired in an electric furnace at 300 ° C. for 2 hours. As a result, BiVO ₄ powder carrying CoO _x as a co-catalyst for oxygen generation was produced.

Preparation of second photocatalyst particles 2-2 (CoOx-supported 0.5% Mo-doped BiVO ₄ particles)
CoOx-supported 0.5% Mo-doped BiVO4 particles were prepared by a solid phase method. Specifically, Bi (NO ₃ ) ₃ (Wako Pure Chemical, 99.9%), V ₂ O ₅ (Wako Pure Chemical, 99.0%) and MoO ₃ (Kanto Chemical, 99.5%) are used as Bi: It put into the menor mortar so that it might become V: Mo = 1: 4.975: 0.025 (mol ratio), Ethanol (10 mL) was added, and it mixed for 30 minutes. The resulting mixture was then placed in a magnetic crucible and baked in an electric furnace at 600 ° C. for 5 hours in the atmosphere. After firing, the fired body was allowed to cool to room temperature to obtain 0.5% Mo-doped BiVO ₄ powder.

0.5 g of the obtained 0.5% Mo-doped BiVO4 powder is put in a magnetic crucible, and Co (NO ₃ ) ₂ (Wako, 99.5%) is put in the magnetic crucible so that CoO is 0.5 wt% as a raw material of the promoter. A small amount of pure water was added. The BiVO ₄ powder was sufficiently suspended by ultrasonic waves and then evaporated to dryness in a hot water bath. Finally, it was fired in an electric furnace at 300 ° C. for 2 hours. As a result, 0.5% Mo-doped BiVO ₄ powder on which CoO _x was supported as a co-catalyst for oxygen generation was produced.

Preparation of second photocatalyst particles 2-3 (0.05% Mo-doped BiVO ₄ particles)
The 0.05% Mo-doped BiVO4 particles were prepared by the liquid solid phase method in the same manner as the second photocatalyst particles 2-1: CoOx-supported BiVO4 particles. Specifically, first, K ₂ CO ₃ (Kanto Chemical, 99.5%), V ₂ O ₅ (Wako Pure Chemical, 99.0%) and MoO3 (Kanto Chemical, 99.5%) were changed to K: V: Mo = It was put into a menor mortar so that it might become 3.03: 4.9975: 0.0025 (mol ratio), and it mixed for 30 minutes after adding ethanol (10 mL). Next, the obtained mixture was put in a magnetic crucible and baked in an electric furnace at 450 ° C. for 5 hours in the atmosphere. After firing, the fired body was allowed to cool to room temperature and then crushed.

The obtained powder was put into a 300 mL Erlenmeyer flask containing 100 ml of water and Bi (NO ₃ ) ₃ · 5H ₂ O (Wako, 99.9%) (Bi: (V + Mo) = 1: 1) at 70 ° C. The mixture was stirred at 1500 rpm for 10 hours using a stir bar. The obtained precipitate was collected by suction filtration, washed with water, and then dried at 60 ° C. for 12 hours in a drier to obtain 0.05% Mo-doped BiVO ₄ powder.

Production of _second photocatalyst particles 2-4 (Ta ₃ N ₅ particles) Ta ₂ O ₅ powder (rare metallic) 1.0 g was used at 850 ° C. in an ammonia stream (flow rate 300 mL / min) using a tubular furnace. Was fired for 20 hours to obtain Ta ₃ N ₅ particles.

(Average primary particle size)
BiVO ₄ particles (second photocatalyst particles 2-1) supported by CoO _x by SEM observation, 0.5% Mo-doped BiVO ₄ particles (second photocatalyst particles 2-2) supported by CoOx, 0.05% Mo-doped BiVO ₄ particles The average primary particle diameters of (second photocatalyst particles 2-3) and Ta ₃ N ₅ particles (second photocatalyst particles 2-4) were calculated. As a result, the average primary particle sizes were about 500 nm, about 500 nm, about 800 nm, and about 300 nm, respectively.

(Band structure)
The band positions of BiVO ₄ were considered as follows with reference to Wang et al., J. Catal. 305-315, 328 (2015).
Top of valence band: -6.8 eV (vs. vacuum level)
Bottom of conduction band: -4.6eV (vs. vacuum level)
The band position of Ta ₃ N ₅ was considered as follows with reference to J. Phys. Chem. B, 2003, 107 (8), 1798-1803.
Upper end of valence band: -5.96 eV (vs. vacuum level)
Bottom of conduction band: -3.86eV (vs. vacuum level)

Preparation of conductive particles
Conductive particles 1
A 10 wt% ethanol dispersion of gold colloid (manufactured by Shinko Chemical Industry) was used. The average primary particle diameter of the gold colloid particles was 20 nm. The average primary particle size is a value published in the catalog as a value calculated by TEM observation. The electronic properties of colloidal gold particles were as follows: work function: 5.1 eV, Fermi level: -5.1 eV (vs. vacuum level) (A. Sharma et al., Applied Physics letters, 93, 163308 (2008) )).

Conductive particles 2
A 10 wt% organic solvent dispersion paste (Okuno Pharmaceutical Co., Ltd.) of ITO colloid (10% Sn-doped In ₂ O ₃ ) was used. The average primary particle diameter of the ITO colloidal particles was 10 nm. In addition, this average primary particle diameter is a value published in the catalog as a value calculated by TEM observation. Moreover, the electronic properties of ITO colloidal particles were: work function: 4.6 eV, Fermi level: -4.6 eV (vs. vacuum level) (A. Sharma et al., Applied Physics letters, 93, 163308 (2008) )).

Conductive particles 3
RuO ₂ particles (manufactured by Shoei Chemical Co., Ltd.) were used. The average primary particle diameter of RuO ₂ particles was 40 nm. The electronic properties of RuO ₂ particles were: work function: 5.0 eV, Fermi level: 5.0 eV (vs. vacuum level) (DJ Yun et al., ACS Appl. Mater. Interfaces, 4, 4588-4594 (2012)).

Conductive particles 4
Ketjen black was used as the carbon particles. The average primary particle diameter of the carbon particles was 40 nm. The electronic characteristics of the carbon particles were: work function: 5 eV, Fermi level: -5.0 eV (vs. vacuum level) (Source: JP 2003-017331 A).

  The raw materials used are shown in Table 1.

Production of photocatalyst material ( production of coating pastes 1 to 33)
The total amount of the first photocatalyst particles (1-1 or 1-2) and the second photocatalyst particles (2-1, 2-2, 2-3, or 2-4) in the ratio shown in Table 2 is Weighed to 0.25 g. This was mixed with 0.75 g of an organic dispersion medium to disperse the photocatalyst particles. As the organic dispersion medium, α-terpineol (manufactured by Kanto Chemical Co., Inc.), 2- (2-butoxyethoxy) ethanol (manufactured by Wako Pure Chemical Industries), and polyacrylic resin (SPB-TE1, manufactured by Soken Chemical Co., Ltd.) are in this order. What was mixed by the ratio of 62.5: 12.5: 25.0 by weight ratio was used. Next, conductive particles (1, 2, 3, or 4) are added at a ratio shown in Table 2 so that the total solid concentration of the first photocatalyst particles, the second photocatalyst particles, and the conductive particles is 25 wt%. Coating pastes 1 to 3, 5 to 12, 14 to 17, 19 to 29, 31, and 32 were prepared. Note that no conductive particles were added to the coating pastes 4, 13, 18, 30, and 33.

(Production of photocatalyst materials 1-30, 33-35)
Screen printing with coating pastes 1 to 33 on a substrate (synthetic quartz glass, size: 5 cm × 5 cm × 1 cm thickness) so that the coating thickness is 60 μm and the coating area is 6.25 cm ² (2.5 cm square) It was applied by the method. Thereafter, the coating pastes 1-2, 5-8, 19-23, and 26-29 containing the conductive particles 1 (gold colloid particles) were dried at 80 ° C. for 30 minutes, and then 300 ° C. or 400 ° C. Were baked for 30 minutes to prepare photocatalyst materials 1-2, 5-8, 19-23, and 26-29. The pastes 3, 9 to 12, 14 to 17, 24, and 32 containing the conductive particles 2 (ITO colloid particles) are dried at 80 ° C. for 30 minutes and then fired at 300 ° C. or 400 ° C. for 30 minutes. Thus, photocatalyst materials 3, 9-12, 14-17, 24, 34 were produced. The coating paste 25 containing the conductive particles 3 (RuO ₂ particles) was dried at 80 ° C. for 30 minutes and then baked at 300 ° C. for 30 minutes to produce a photocatalyst material 25. The coating paste 31 containing the conductive particles 4 (carbon) was dried at 80 ° C. for 30 minutes and then baked at 300 ° C. for 30 minutes to produce a photocatalyst material 33. For coating pastes 4, 13, 18, 30, 33 that do not contain conductive particles, after drying at 80 ° C. for 30 minutes, firing at 300 ° C. for 30 minutes and photocatalyst materials 4, 13, 18, 30, 35 was produced. The thickness of the photocatalyst layer after firing was 10 μm in all cases.

  As the conductive particles 1 (gold colloid particles), those having an average particle diameter of 20 nm were used. On the other hand, for example, if the content of the conductive particles 1 is more than a predetermined amount, the conductive particles 40 tend to aggregate and exist when applied to the substrate 90. Therefore, when the photocatalyst layer 70 is formed by heating, the conductive particles 40 are bonded to each other. For example, in the photocatalyst material 8 in which the content of the conductive particles 40 is 50 wt%, the conductive particles 40 are bonded to each other, and the particle diameter of the conductive particles 40 in the photocatalyst layer is approximately 200 nm.

  The photocatalyst materials 1 to 3, 5 to 7, 9 to 12, 14 to 17, 19 to 20, 24, 26, 27, 33, and 34 have a structure corresponding to the photocatalyst material 100 shown in FIG.

  In photocatalyst material 8, 21-23, 28, 29, the some electroconductive particle 40 joins, and the particle diameter of the electroconductive particle in a photocatalyst layer is larger than the particle diameter of the electroconductive particle in a paste. The photocatalyst materials 8, 21 to 23, 28, and 29 have a structure corresponding to the photocatalyst material 104 shown in FIG. In these photocatalyst materials, the conductive particles and the first and second photocatalyst particles are joined, and the photocatalyst layer 70 has a network structure.

  The photocatalyst material 25 has a structure corresponding to the photocatalyst material 105 shown in FIG. The photocatalyst material 25 is connected to the first photocatalyst particle 10 and the second photocatalyst particle 20 in a state where the conductive particles 40 are aggregated.

(Preparation of photocatalyst material 31)
The paste 18 was applied to the substrate, dried at 80 ° C. for 30 minutes, and then fired at 300 ° C. for 30 minutes to obtain a photocatalyst film. Thereafter, the photocatalyst film is divided into five conductive layers so that the amount of colloidal gold particles is 2 wt% when the total amount of the first photocatalyst particles and the second photocatalyst particles is 100 wt%. The colloidal particles 1 were dropped to obtain a colloidal gold particle-containing photocatalyst film. The gold colloidal particle-containing photocatalyst film was dried at room temperature for 10 minutes and further at 80 ° C. for 30 minutes, and then calcined at 300 ° C. for 30 minutes to produce a photocatalyst material 31. The photocatalyst material 31 has a structure corresponding to the photocatalyst material 100 shown in FIG.

(Preparation of photocatalytic material 32)
Paste 18 was applied to the substrate. Next, a paste in which the amount of gold colloid particles was 100% by weight was prepared, and a paste containing gold colloid particles was further applied to the surface of the base material on which the paste 18 was applied. This was dried at room temperature for 10 minutes and further at 80 ° C. for 30 minutes, and then baked at 300 ° C. for 30 minutes to produce a film in which the photocatalyst film was coated with a gold colloid film on the surface of the substrate. A glass substrate with a carbon tape attached was prepared. The photocatalyst film was peeled from the substrate by pressing so that the surface of the photocatalyst film was in contact with the carbon tape on the glass substrate. Thereby, the photocatalyst film | membrane was transferred to the glass substrate which affixed the carbon tape, and the photocatalyst material 32 was produced by forming a photocatalyst layer.

  The photocatalyst material 32 has a structure in which a gold colloid film and a photocatalyst film are laminated in this order on a glass substrate via a carbon tape. The photocatalyst material 32 has a structure corresponding to the structure in which the intermediate layer 80 is further provided between the base material 90 and the photocatalyst layer 70 in the photocatalyst material 104 shown in FIG. In the photocatalyst material 32, the glass substrate corresponds to the base material 90, the gold colloid film corresponds to the intermediate layer 80, and the photocatalyst film corresponds to the photocatalyst layer 70.

Production of photocatalyst materials 36 to 49 having a coating portion ( production of coating paste)
The first photocatalyst particles (1-1) and the second photocatalyst particles (2-3) were weighed so that the total amount was 0.25 g. This was mixed with 0.75 g of an organic dispersion medium to disperse the photocatalyst particles. As the organic dispersion medium, α-terpineol (manufactured by Kanto Chemical Co., Inc.), 2- (2-butoxyethoxy) ethanol (manufactured by Wako Pure Chemical Industries), and polyacrylic resin (SPB-TE1, manufactured by Soken Chemical Co., Ltd.) are in this order. What was mixed by the ratio of 62.5: 12.5: 25.0 by weight ratio was used. Next, conductive particles (1, 2 or 4) are added, and three types of coatings are applied so that the total solid concentration of the first photocatalyst particles, the second photocatalyst particles, and the conductive particles is 25 wt%. A paste was prepared. Specifically, the paste containing the first photocatalyst particles (1-1), the second photocatalyst particles (2-3), and the conductive particles 1 or the conductive particles 2 is 40 wt% and 40 wt% in this order. In the paste containing the conductive particles 4 at 20 wt%, the order was 47.5 wt%, 47.5 wt%, and 5 wt%.

(Production of photocatalyst materials 36 to 49)
Screen printing method using the above three types of coating paste on a substrate (synthetic quartz glass, size: 5cm x 5cm x thickness 1cm) so that the coating thickness is 60μm and the coating area is 6.25cm ² (2.5cm square) It was applied with. Then, about the paste for application | coating containing the electroconductive particle 1 (gold colloid particle), after making it dry for 30 minutes at 80 degreeC, it baked for 30 minutes at 300 degreeC, and produced the photocatalyst materials 36-45. The coating paste containing the conductive particles 2 (ITO colloidal particles) was dried at 80 ° C. for 30 minutes and then baked at 400 ° C. for 30 minutes to produce photocatalyst materials 46 and 47. The coating paste containing the conductive particles 4 (carbon) was dried at 80 ° C. for 30 minutes and then baked at 300 ° C. for 30 minutes to produce photocatalyst materials 48 and 49. The thickness of the photocatalyst layer after firing was 10 μm.

(Production of photocatalyst materials 36 to 49 having covering portions)
Covering portions were formed using the materials shown in Table 3 for the photocatalyst materials 36 to 44, 46, and 48. The arrangement of the coating portion on the photocatalyst material was performed according to the following procedure. First, in the photocatalyst materials 38 to 43, an alcohol solution of a 20 mM metal monomer (alkoxide, chloride, nitrate) shown in Table 3 is formed on the surface of the photocatalyst layer, and in the photocatalyst materials 36 and 37, 0.4 wt% metal oxide. 50 to 200 μL of colloidal alcohol dispersion was uniformly dropped. Then, it was made to dry at 100 degreeC for 30 minutes, and the coating part was formed in the photocatalyst layer surface. The arrangement of the coating portion of the photocatalyst material 44 shown in Table 3 is generally a monomolecular layer on the surface of the conductive fine particles by immersing the photocatalyst material in 3 mL of a 20 mM toluene solution of 3-mercaptopropyltriethoxysilane at room temperature for 3 hours. Then, the photocatalyst material was pulled up from the solution, washed 5 times with toluene, and dried at 120 ° C. for 30 minutes to form a coating on the surface of the conductive particles. In addition, the coating part was not formed about the photocatalyst materials 45, 47, and 49.

In the photocatalyst material 36, water and ethanol mixed solution (solid content 0.4 wt%) of α-Fe ₂ O ₃ colloid having an average primary particle size of about 10 nm was used as a ferric trioxide (Fe ₂ O ₃ ) colloid sol.
In the photocatalyst material 37, water and ethanol mixed solution (solid content 0.4 wt%) of CeO ₂ colloid having an average primary particle diameter of about 8 nm was used as the cerium oxide (CeO ₂ ) sol.

Evaluation
The structure of the photocatalyst layer With respect to the photocatalyst material produced, the structure of the photocatalyst layer was observed by SEM. The results are shown in FIGS. FIG. 11 is a surface observation image of the photocatalyst layer 70 in the photocatalyst material 3. FIG. 12A to FIG. 12E are surface observation images of the photocatalyst layer 70 in the photocatalyst materials 14 to 18. FIG. 13 is a surface observation image of the photocatalyst layer 70 in the photocatalyst material 25. The surface observation image is an image obtained by observing a plane perpendicular to the stacking direction (Z-axis direction) from the substrate toward the photocatalyst layer 70.

  As shown in FIGS. 11 to 13, it was confirmed that the photocatalytic layer 70 had pores 71. In the photocatalyst materials 3, 14 to 17 and 25, it was confirmed that the first photocatalyst particles 10 and the second photocatalyst particles 20 were in physical contact with the conductive particles 40 in the photocatalyst layer 70. . Further, as shown in FIG. 13, it was confirmed that the conductive particles 40 were aggregated in the photocatalyst material 25. As will be described later, in the photocatalyst material 25, the conductive particles 40 are agglomerated, but good water splitting activity could be obtained.

Photocatalytic activity (water splitting activity) of photocatalyst material
Next, the photocatalytic activity (water splitting activity) of each of the produced photocatalyst materials 1 to 35 by visible light irradiation was evaluated by the following method. A photocatalyst material and 100 ml of ultrapure water were placed in a glass flask with a window for upward irradiation made of Pyrex (registered trademark) to prepare a reaction solution. The glass flask containing the reaction solution was attached to a closed circulation device (Makuhari Chemical Co., Ltd.), and the atmosphere in the reaction system was replaced with argon. The argon pressure was 90 torr. Visible light was irradiated from the Pyrex (registered trademark) window side by a 300 W xenon lamp (manufactured by Cermax, PE-300BF) equipped with a UV cut filter (L-42, manufactured by HOYA). The amount of hydrogen generated by reduction of water and the amount of oxygen generated by oxidation of water for 3 hours after light irradiation was measured using a gas chromatograph (manufactured by Shimadzu Corporation, GC-8A, TCD detector, MS- 5A column). The results were as shown in Table 2. In addition, only in the photocatalyst material 29, the photocatalytic activity was evaluated using AM1.5G simulated sunlight as a light source.

(Test using first photocatalyst particle 1-1 and second photocatalyst particle 2-1)
14 to 17 show the relationship between the photocatalyst materials 1 to 4 and the hydrogen and oxygen generation efficiency (generation rate). As shown in FIG. 17, in the photocatalyst material 4 containing no conductive particles, generation of oxygen could not be confirmed. As shown in Table 2, the hydrogen generation rate was as low as 0.09 μmol / hr. On the other hand, as shown in FIGS. 14 to 16, in the photocatalyst materials 1 to 3 containing conductive particles, it was confirmed that the generation rates of oxygen and hydrogen were remarkably increased. In particular, regarding the hydrogen generation rate, the hydrogen generation rates of the photocatalyst materials 1 and 2 containing gold colloid particles as conductive particles were about 2-3 times that of the photocatalyst material 4. It was confirmed that the hydrogen generation rate of the photocatalyst material 3 containing ITO colloidal particles as conductive particles was 20 times that of the photocatalyst material 4. Further, from the comparison of the photocatalyst material 4 and the photocatalyst material 3, ITO cannot be a promoter for hydrogen generation, but has a function as conductive particles in the present invention, and the photocatalyst material has a hydrogen generation ability. It was confirmed that it was significantly improved.

  The gas generation speed in each photocatalyst material 1-4 is shown in FIG. As shown in Table 2 and FIGS. 14 and 15, in the photocatalyst materials 1 and 2 using Au colloid as the conductive particles, the hydrogen gas generation rate is 0.23 μmol / hr, and the oxygen gas generation rate is 0.11 to 0. It was as high as 12 μmol / hr. In the photocatalyst material 3 using ITO colloidal particles, very high values were obtained for both the hydrogen gas generation rate and the oxygen gas generation rate. The conductive particles 1 used in the photocatalyst materials 1 and 2 are gold colloids, and the conductive particles 2 used in the photocatalyst material 3 are ITO. The specific gravity of ITO is smaller than that of Au. Therefore, for example, in the photocatalyst materials 1 and 3, the weight ratio of the conductive particles contained in the photocatalyst layer is 20 wt%, but the photocatalyst material 3 has a larger volume ratio than the photocatalyst material 1. .

(Test using first photocatalyst particle 1-1 and second photocatalyst particle 2-2 (i) Au colloidal particle)
FIG. 19 shows hydrogen and oxygen generation efficiencies for the photocatalyst materials 5 to 8 and the photocatalyst material 13 in which the addition amount of the conductive particles 1 is different. In FIG. 19, the photocatalyst material 13 that does not contain conductive particles and the photocatalyst materials 5 to 8 that contain 5, 10, 20, and 50 wt% of the conductive particles 1 (Au colloidal particles) in this order from the left.

  In the photocatalyst material 13 containing no conductive particles, as shown in Table 2, generation of oxygen could not be confirmed. The hydrogen generation rate was as low as 0.12 μmol / hr.

  On the other hand, in the photocatalyst materials 5 to 8 containing Au colloidal particles as conductive particles, it was confirmed that the generation rates of oxygen and hydrogen increased dramatically. The hydrogen generation rate of the photocatalyst materials 5 to 8 was about 2.5 times to about 27 times that of the photocatalyst material 13. In addition, in the photocatalyst material 8 in which the content of the conductive particles 1 is 50%, it is considered that the amount of the conductive particles is large and they are bonded in the photocatalyst layer. In the photocatalyst materials 5 to 8, the water splitting performance was the highest in the photocatalyst material 7 in which the content of Au colloidal particles was 20% by weight.

(Test using first photocatalyst particle 1-1 and second photocatalyst particle 2-2 (ii) ITO colloid particle)
FIG. 20 shows hydrogen and oxygen generation efficiencies for the photocatalyst materials 9 to 12 and the photocatalyst material 13 in which the addition amount of the conductive particles 2 is different. In FIG. 20, the photocatalyst material 13 containing no conductive particles and the photocatalyst materials 9 to 12 containing 5, 10, 20, and 50 wt% of the conductive particles 2 (ITO colloidal particles) are shown in order from the left.

  In the photocatalyst materials 9 to 12 containing ITO colloidal particles as conductive particles, it was confirmed that the generation rates of oxygen and hydrogen increased dramatically. It was confirmed that the hydrogen generation rate of the photocatalyst materials 9 to 12 was about 4 to about 44 times that of the photocatalyst material 13. Moreover, in photocatalyst materials 9-12, the water decomposition performance was the largest in the photocatalyst material 11 with the content of ITO colloidal particles of 20% by weight, and the water decomposition performance was flat at 20% by weight or more.

From Table 2, FIGS. 19 and 20, by adding conductive particles to the photocatalyst layer containing 3% Rh-doped SrTiO ₃ particles as the first photocatalyst particles and CoOx-supported BiVO ₄ particles as the second photocatalyst particles, the photocatalyst is added. It was confirmed that the activity was dramatically improved. In addition, since the generation rate of oxygen and hydrogen fluctuated depending on the amount of conductive particles added, optimization of the amount of conductive particles added improves conductivity and reduces the pore diameter that enables gas diffusion. It is considered that the photocatalytic activity can be optimized by harmonizing with the balance.

(Test using the first photocatalyst particles 1-1 and the second photocatalyst particles 2-3 (i) _ITO colloidal particles)
FIG. 21 shows hydrogen and oxygen generation efficiencies for the photocatalyst materials 14 to 18 having different amounts of the conductive particles 2 added. In FIG. 21, the photocatalyst material 18 that does not include conductive particles and the photocatalyst materials 14 to 17 that include 5, 10, 20, and 50 wt% of the conductive particles 2 (ITO colloidal particles) in this order from the left.

  In the photocatalyst material 18 containing no conductive particles, as shown in Table 2, generation of oxygen could not be confirmed. The hydrogen generation rate was as low as 0.20 μmol / hr.

  On the other hand, in the photocatalyst materials 14 to 17 containing the ITO colloidal particles as the conductive particles, it was confirmed that the generation rates of oxygen and hydrogen increased dramatically. The hydrogen generation rate of the photocatalyst materials 14 to 17 was about 5 times to about 11 times that of the photocatalyst material 18.

  In addition, as described above, the hydrogen generation rates of the photocatalyst materials 14 to 17 were significantly larger than those of the photocatalyst material 18, and the oxygen and hydrogen generation rates varied depending on the amount of conductive particles added. In addition, as shown in FIG. 12D, the present inventors have confirmed through experiments that a gap exists in the photocatalyst layer of the photocatalyst material 17. From the above, it is considered that by optimizing the addition amount of the conductive particles, the balance between the improvement of conductivity and the reduction of the pore diameter enabling gas diffusion can be harmonized and the photocatalytic activity can be optimized. .

(Test using first photocatalyst particles 1-1 and second photocatalyst particles 2-3 (ii) carbon)
Table 2 shows the hydrogen and oxygen production efficiency of the photocatalyst material 33 containing the conductive particles 4 (carbon). It was confirmed that the photocatalyst material 33 containing carbon as the conductive particles has increased oxygen and hydrogen generation rates in comparison with the photocatalyst material 18 not containing the conductive particles. The hydrogen generation rate of the photocatalyst material 33 was about four times that of the photocatalyst material 18.

(Test using first photocatalyst particles 1-2 and second photocatalyst particles 2-3_Au colloidal particles (i))
FIG. 22 shows hydrogen and oxygen generation efficiencies for the photocatalyst materials 19 to 23 and 30 having different amounts of the conductive particles 1 added. In FIG. 22, in order from the left, the photocatalyst material 30 containing a conductive particle that does not contain conductive particles and the conductive particles 1 (Au colloidal particles) produced at a firing temperature of 300 ° C., and 10, 20, 30, 40, and 50 wt%. It is material 19-23.

  In the photocatalyst material 30 containing no conductive particles, as shown in Table 2, the oxygen generation rate was as low as 0.04 μmol / hr, and the hydrogen generation rate was as low as 0.05 μmol / hr.

  On the other hand, in the photocatalyst materials 19 to 23 containing Au colloidal particles as conductive particles, it was confirmed that the generation rates of oxygen and hydrogen increased dramatically. It was confirmed that the hydrogen generation rate of the photocatalyst materials 19 to 23 was about 63 times to about 308 times that of the photocatalyst material 30. In the photocatalyst materials 19 to 23, the gas generation rate was the highest when the content of Au colloidal particles was 40% by weight. Furthermore, since the generation rate of oxygen and hydrogen fluctuated depending on the amount of conductive particles added, optimization of the amount of conductive particles added improves conductivity and reduces the pore diameter that enables gas diffusion. It is considered that the photocatalytic activity can be optimized by harmonizing with the balance. In addition, in the photocatalyst materials 21 to 23 in which the content of conductive particles is 30 wt% or more, a plurality of conductive particles are bonded in the photocatalyst layer 70.

(Test using first photocatalyst particles 1-2 and second photocatalyst particles 2-3_Au colloidal particles (ii))
FIG. 23 shows the hydrogen and oxygen production efficiencies for the photocatalyst materials 26 to 28 in which the addition amount of the conductive particles 1 is different. In FIG. 23, the photocatalyst materials 26 to 28 containing the conductive particles 1 (Au colloidal particles) produced at a firing temperature of 400 ° C. in order from the left.

  In the photocatalyst materials 26 to 28 containing Au colloidal particles as conductive particles, it was confirmed that the generation rates of oxygen and hydrogen were dramatically increased. It was confirmed that the hydrogen generation rate of the photocatalyst materials 26 to 28 was about 50 times to about 57 times that of the photocatalyst material 30.

(Test using first photocatalyst particles 1-2 and second photocatalyst particles 2-3_various conductive particles)
FIG. 24 shows hydrogen and oxygen generation efficiencies for the photocatalyst materials 19, 24, 25, and 30 having different kinds of conductive particles. In FIG. 24, in order from the left, photocatalyst material 30 that does not contain conductive particles, and photocatalyst materials 19, 24, and 25 each containing 10% by weight of Au colloid particles, ITO colloid particles, and RuO ₂ colloid particles as conductive particles. is there.

According to Table 2 and FIG. 24, different types of electrical conductivity were obtained in the photocatalyst layer containing 4% La and 4% Rh doped SrTiO ₃ particles as the first photocatalyst particles and 0.05% Mo doped BiVO ₄ particles as the second photocatalyst particles. It was confirmed that the photocatalytic activity of the photocatalyst materials 19, 24, and 25 to which the conductive particles were added was dramatically improved as compared with the photocatalyst material 30 that did not contain conductive particles.

(Test using first photocatalyst particles 1-2 and second photocatalyst particles 2-3_various light sources)
FIG. 25 shows the gas generation efficiency for the photocatalyst materials 22 and 29 with different light sources. In FIG. 25, the photocatalyst material 22 irradiated with the xenon lamp and the photocatalyst material 29 irradiated with AM1.5 pseudo-sunlight in this order from the left.

  From Table 2 and FIG. 25, the photocatalyst materials 22 and 29 including the first photocatalyst particles, the second photocatalyst particles, and the conductive particles are not compared with the photocatalyst material 30 including no conductive particles regardless of the type of the light source. Thus, it was confirmed that the generation rates of oxygen and hydrogen increased dramatically. It was confirmed that the hydrogen generation rates of the photocatalyst materials 22 and 29 were about 308 times and about 200 times that of the photocatalyst material 30, respectively.

(Test using first photocatalyst particles 1-2 and second photocatalyst particles 2-3_addition after conductive particles (i))
As shown in Table 2, even the photocatalyst material 31 in which the conductive particles 1 are further added to the photocatalyst material 18 that does not contain conductive particles in a later step has a photocatalytic activity that is about 17 times higher than that of the photocatalyst material 18. Expression was confirmed.

(Test using first photocatalyst particles 1-2 and second photocatalyst particles 2-3_addition after conductive particles (ii))
As shown in Table 2, a photocatalyst material 32 in which a layer containing conductive particles is formed between the base material and the photocatalyst layer of the photocatalyst material 18 that does not contain conductive particles is used as an intermediate layer. In addition, it was confirmed that the photocatalytic activity was about 3 times higher than that of the photocatalytic material 18.

(Test using first photocatalyst particles 1-1 and second photocatalyst particles 2-4_ITO colloidal particles)
Table 2 shows the hydrogen and oxygen production efficiencies of the photocatalyst material 34 containing ITO as the conductive particles and the photocatalyst material 35 containing no conductive particles. In the photocatalyst material 35 containing no conductive particles, generation of hydrogen and oxygen was not confirmed. On the other hand, generation of hydrogen and oxygen was confirmed in the photocatalyst material 34 containing conductive particles.

  As described above, the photocatalyst material including the first photocatalyst particles, the second photocatalyst particles, and the conductive particles connecting the first photocatalyst particles and the second photocatalyst particles via the first photocatalyst particles is very excellent. Oxygen and hydrogen production efficiency, that is, photocatalytic activity was confirmed.

(Test of photocatalyst material with coating)
Structure The structure of the produced photocatalyst material was observed. The photocatalyst materials 36 and 37 have the structure shown in FIG. 3, the photocatalyst materials 38 to 43 have the structure shown in FIG. 4, and the photocatalyst material 44 has the structure shown in FIG. . Further, the thickness of the produced photocatalyst material was as shown in Table 3.

Photocatalytic activity (water splitting activity) of photocatalyst material
Relationship between material of covering portion and hydrogen generation activity (reverse reaction prevention rate based on hydrogen generation rate) A test for confirming the reverse reaction prevention effect was performed as follows. First, the production rate of hydrogen and oxygen is measured under reduced pressure so that the reverse reaction does not easily occur. Thereafter, the atmospheric pressure is increased to half normal pressure, and the production rates of hydrogen and oxygen are measured in an environment where a reverse reaction can occur. Here, the reduced pressure environment was set to 80 torr, and the semi-normal pressure environment was set to 380 torr. Then, as shown in the following formula, the percentage of the generation rate under semi-normal pressure (380 torr) with respect to the generation rate under reduced pressure (80 torr) was calculated as a reverse reaction prevention rate (%). That is, when the reverse reaction is completely prevented by the formation of the coating portion, the hydrogen and oxygen production rates under the reduced pressure and the semi-normal pressure are the same value, and the reverse reaction prevention rate is 100%.
Reverse reaction prevention rate (%) = Generation rate under semi-normal pressure (380 torr) (μmol / hr) / Generation rate under reduced pressure (80 torr) (μmol / hr) × 100

Hydrogen generation rate under reduced pressure (80 torr) and hydrogen generation rate under semi-normal pressure (380 torr) of a plurality of photocatalyst materials that commonly contain Au colloidal particles as conductive particles and have different coating materials Table 3 shows the rate (μmol / hr) and the reverse reaction prevention rate (%). Further, FIG. 26 shows the relationship between the material of the covering portion and the reverse reaction prevention rate based on the hydrogen generation rate. Each of the photocatalyst materials 36 to 44 shows a high reverse reaction prevention rate compared to the photocatalyst material 45 having no coating portion, and includes ferric trioxide (Fe ₂ O ₃ ), silica (SiO ₂ ), zirconium oxide ( In the case where ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ), cerium oxide (CeO ₂ ), or a silane coupling agent (3-mercaptopropyltriethoxysilane) is used as the coating part, the reverse reaction on the Au particle surface It was confirmed that the prevention effect was obtained. The reverse reaction prevention rate of the photocatalyst materials 37 to 43 was as high as 70% or more, and among them, the reverse reaction prevention rate of the photocatalyst material 40 exceeded 80% and was higher. Thereby, when zirconium oxide (ZrO ₂ ) was used as the material for the covering portion, it was confirmed that a high reverse reaction preventing effect was obtained. In addition, the photocatalyst materials 36, 38, and 39 have a higher hydrogen generation rate under reduced pressure than the photocatalyst material 45, and it was confirmed that these photocatalyst materials originally had an excellent hydrogen generation ability. Since a reverse reaction is unlikely to occur under reduced pressure, a high hydrogen generation rate under reduced pressure is considered to be that the photocatalyst material originally has an excellent hydrogen generation ability, which is very important. From the above, when ferric trioxide (Fe ₂ O ₃ ) and zirconium oxide (ZrO ₂ ) are used as the covering material, a high reverse reaction preventing effect can be obtained and a high hydrogen generation ability can be obtained. confirmed.

Relationship between the material of the covering portion and the oxygen generation activity (reverse reaction prevention rate based on the oxygen generation rate) In the same manner as the method for evaluating the hydrogen generation activity described above, Au colloidal particles are commonly used as the conductive particles and coated The oxygen generation rate under reduced pressure (80 torr) (μmol / hr), the oxygen generation rate under half normal pressure (380 torr) (μmol / hr), and the reverse reaction prevention rate (e.g. %). The results are shown in Table 3. Further, FIG. 27 shows the relationship between the material of the covering portion and the reverse reaction prevention rate based on the hydrogen generation rate. Each of the photocatalyst materials 36 to 44 shows a high reverse reaction prevention rate compared to the photocatalyst material 45 having no coating portion, and includes ferric trioxide (Fe ₂ O ₃ ), silica (SiO ₂ ), zirconium oxide ( When ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ), cerium oxide (CeO ₂ ), or a silane coupling agent (3-mercaptopropyltriethoxysilane) is used as a material for the coating portion, It was confirmed that a reverse reaction preventing effect was obtained. The photocatalyst materials 38 and 40 have a particularly high reverse reaction prevention rate, and it has been confirmed that when zirconium oxide (ZrO ₂ ) is used as a material for the covering portion, a high reverse reaction prevention effect can be obtained. In addition, the photocatalyst materials 36 and 39 had a higher oxygen generation rate under reduced pressure than the photocatalyst material 45, and it was confirmed that these photocatalyst materials originally had an excellent oxygen generation ability. Since a reverse reaction is unlikely to occur under reduced pressure, a high oxygen generation rate under reduced pressure is considered to be that the photocatalyst material originally has an excellent oxygen generation capability, which is very important. From the above, when ferric trioxide (Fe ₂ O ₃ ) and zirconium oxide (ZrO ₂ ) are used as the covering material, a high reverse reaction preventing effect can be obtained and a high hydrogen generation ability can be obtained. confirmed.

Relationship between content of zirconium oxide and hydrogen generation activity (reverse reaction prevention rate based on hydrogen generation rate) Content of zirconium oxide as a material of the coating part, that is, photocatalyst materials 38 to 41 having different thicknesses of the coating part, FIG. 28 shows the hydrogen generation efficiency (hydrogen generation rate under reduced pressure (80 torr) (μmol / hr) and reverse reaction prevention rate (%)) for the photocatalyst material 45 that does not include the coating portion. In FIG. 28, in order from the left, photocatalyst material 45 that does not include a coating portion, and photocatalyst materials 38 to 41 having a coating portion (zirconium oxide) thickness of 1, 2, 4, and 8 nm.

  In the photocatalyst material 45 that does not include the coating portion, as shown in Table 3, the amount of oxygen generated under reduced pressure was 2.88 μmol / hr, whereas the reverse reaction prevention rate was 54%. Was low

  On the other hand, in the photocatalyst materials 38 to 41 containing Au colloidal particles as conductive particles and having different thicknesses of the zirconium oxide coating portions, when the thickness of the coating portions is 4 nm or less, hydrogen under reduced pressure is used. Although the generation rate did not decrease so much, the hydrogen generation rate greatly decreased as the thickness increased to 8 nm. Moreover, the reverse reaction prevention rate increased according to thickness until the thickness of the coating | coated part was 4 nm. On the other hand, when the thickness of the covering portion was as thick as 8 nm, the reverse reaction prevention rate decreased. As mentioned above, when forming a coating | coated part from a metal monomer, it was confirmed that the thickness is less than 10 nm.

Relation between content of zirconium oxide and oxygen generation activity (reverse reaction prevention rate based on oxygen generation rate) Content of zirconium oxide as a material of the covering portion, that is, photocatalyst materials 38 to 41 having different thicknesses of the covering portion, FIG. 29 shows the oxygen generation efficiency (oxygen generation rate under reduced pressure (80 torr) (μmol / hr) and reverse reaction prevention rate (%)) for the photocatalyst material 45 that does not include the coating portion. In FIG. 29, in order from the left, photocatalyst material 45 that does not include a coating portion, and photocatalyst materials 38 to 41 having a coating portion (zirconium oxide) thickness of 1, 2, 4, and 8 nm.

  In the photocatalyst material 45 not including the coating portion, as shown in Table 3, the amount of oxygen generated under reduced pressure was 1.26 μmol / hr, whereas the reverse reaction prevention rate was 56%. Was low

  On the other hand, in the photocatalyst materials 38 to 41 containing Au colloidal particles as the conductive particles and having different thicknesses of the zirconium oxide coating portions, the oxygen under reduced pressure is obtained when the thickness of the coating portions is 4 nm or less. Although the generation rate did not decrease so much, the oxygen generation rate greatly decreased when the thickness increased to 8 nm. Moreover, the reverse reaction prevention rate generally increased in accordance with the thickness until the thickness of the covering portion was 4 nm. On the other hand, when the thickness of the covering portion was as thick as 8 nm, the reverse reaction prevention rate decreased. As mentioned above, when forming a coating | coated part from a metal monomer, it was confirmed that the thickness is less than 10 nm.

10 Visible light-responsive photocatalyst particles for hydrogen generation (first photocatalyst particles)
20 Visible light-responsive photocatalyst particles for oxygen generation (second photocatalyst particles)
40 Conductive Particles 50 Conductive Wire 60 Covering Unit 61 Colloidal Particles 62 and 63 Reverse Reaction Prevention Layer 70 Photocatalyst Layer 71 Pore 80 Intermediate Layer 90 Base Material 100 to 105, 110, 120, 130 Photocatalyst Material

Claims (20)

A photocatalyst material comprising a substrate and a photocatalyst layer immobilized on the substrate,
The photocatalytic layer is
Visible light responsive first photocatalyst particles for hydrogen generation;
A second photocatalyst particle of visible light responsive type for oxygen generation;
The second photocatalyst particle is provided between the first photocatalyst particle and the second photocatalyst particle and is at a position that is more negative than the electron energy level at the top of the valence band of the first photocatalyst particle. Conductive particles having a Fermi level at a position more positive than the electron energy level at the bottom of the conduction band of the material and capable of storing electrons and holes,
In the photocatalyst layer, the conductive particles are arranged to be connected to the first photocatalyst particles and the second photocatalyst particles. The conductive particles have a first region, a second region, and a third region on a surface thereof; and
Contacting the first photocatalytic particles in the first region;
Contacting the second photocatalytic particles in the second region;
2. The photocatalyst material according to claim 1, wherein the photocatalyst material does not contact any of the first and second photocatalyst particles in the third region. The photocatalyst material of Claim 1 or 2 whose electrical conductivity of the said electroconductive particle is 0.1 Scm < ^-1 > or more.   The average primary particle diameter of the conductive particles is smaller than the average primary particle diameter of the first photocatalyst particles and smaller than the average primary particle diameter of the second photocatalyst particles. The photocatalyst material according to claim 1.   The photocatalyst material as described in any one of Claims 1-4 whose average primary particle diameter of the said electroconductive particle is 10 nm or more and 200 nm or less.   The content of the conductive particles is 5 wt% or more and 50 wt% or less with respect to the total content of the first photocatalyst particles, the second photocatalyst particles, and the conductive particles. The photocatalyst material as described in any one.   The photocatalyst material as described in any one of Claims 1-6 in which the material of the said electroconductive particle contains a conductive metal oxide.   The photocatalyst material according to claim 7, wherein the conductive metal oxide includes tin-doped indium oxide (ITO).   The photocatalyst material as described in any one of Claims 1-6 whose material of the said electroconductive particle contains a metal.   The photocatalyst material of Claim 9 in which the said metal contains gold | metal | money.   The photocatalyst material as described in any one of Claims 1-6 whose material of the said electroconductive particle contains a carbon material.   The photocatalyst material according to claim 11, wherein the carbon material includes one or more selected from the group consisting of carbon black, ketjen black, acetylene black, channel black, furnace black, thermal black, and lamp black.   The photocatalyst material according to any one of claims 1 to 12, further comprising an intermediate layer between the base material and the photocatalyst layer.   The photocatalyst material according to any one of claims 1 to 13, wherein a promoter is supported on the surface of the first photocatalyst particles and / or the second photocatalyst particles.   The photocatalyst material of Claim 14 whose average primary particle diameter of the said promoter is less than 10 nm.   The photocatalyst material as described in any one of Claims 1-15 used for the photolysis reaction of the water by visible light.   A photocatalyst module for water splitting, comprising the photocatalyst material according to claim 16.   A hydrogen production system comprising the photocatalyst module for water splitting according to claim 17. A method for producing a photocatalyst material comprising the base material according to any one of claims 1 to 16 and a photocatalyst layer fixed to the base material,
Visible light responsive first photocatalyst particles for hydrogen generation, visible light responsive second photocatalyst particles for oxygen generation, and negative electron energy level at the top of the valence band of the first photocatalyst particles Conductive particles having a Fermi level at a position that is more positive than the electron energy level at the lower end of the conduction band of the second photocatalyst particle and capable of storing electrons and holes are wet-dispersed in a solvent. Applying the dispersion to the substrate;
Drying the dispersion applied to the substrate;
A method comprising: at least. A method for producing a photocatalyst material comprising the base material according to any one of claims 1 to 16 and a photocatalyst layer fixed to the base material,
A step of applying a first dispersion obtained by wet-dispersing a visible light responsive first photocatalyst particle for hydrogen generation and a second photocatalyst particle for visible light response for oxygen generation in a solvent to the substrate. When,
It has a Fermi level at a position that is more negative than the electron energy level at the upper end of the valence band of the first photocatalyst particle and at a position that is more positive than the electron energy level at the lower end of the conduction band of the second photocatalyst particle. Applying a second dispersion containing conductive particles capable of storing electrons and holes to a substrate to which the first dispersion is applied;
A method comprising: at least.